Learn Hardcore German: Wenn ich über all diese Themen schreibe, merke ich: Sowohl Medien als auch Emotionen haben Macht, aber wir können lernen, bewusst damit umzugehen. - When I write about all these topics, I realize: both media and emotions have power, but we can learn to deal with them consciously.

In the main clause after the comma, the verb goes in second position, so we get merke ich (verb first, then subject) to keep the verb in position 2 of that clause:
Wenn ich … schreibe, merke ich …

Why is it wenn here and not als or wann?

wenn = whenever / if (for present or repeated events, or general conditions)
→ Wenn ich über all diese Themen schreibe = Whenever I write about all these topics…
als = when for a single event in the past
→ Als ich über alle diese Themen schrieb, merkte ich … (one specific time in the past)
wann = when? in questions or indirect questions
→ Wann schreibst du über diese Themen? – When do you write about these topics?

So wenn is correct here because it’s a general / repeated situation, not one specific past event and not a question.

Why is it über all diese Themen and not something like von all diesen Themen?

With schreiben in the sense of “to write about something”, German normally uses über + accusative:

über ein Thema schreiben – to write about a topic
über Politik schreiben – to write about politics

von is possible with schreiben von but it tends to mean more “to write of / from (the perspective of), to mention” and sounds a bit different in nuance.
For a neutral “write about”, über is the standard and most natural choice: über all diese Themen.

Why is it all diese Themen and not alle diese Themen?

Both alle diese Themen and all diese Themen are used in modern German and are generally understood the same.

Traditionally, alle is the fully declined form and alle diese Themen is a bit more formal/standard. all without -e is very common in everyday language, especially before another determiner like diese:

all diese Leute / alle diese Leute
all diese Probleme / alle diese Probleme

So über all diese Themen is normal, especially in less formal writing. If you want to be very textbook-precise, you can remember alle diese Themen as the “safe” version.

Why is there a colon after merke ich: instead of a comma and dass?

The colon is used to introduce what the speaker realizes / notices. You can think of it like:

Ich merke: [Folgendes] – I notice: [the following]

This is mostly stylistic. You could also write:

Wenn ich über all diese Themen schreibe, merke ich, dass sowohl Medien als auch Emotionen Macht haben, …

Using dass makes it a standard subordinate clause; using a colon makes the statement after it sound a bit more direct and emphatic, almost like a small conclusion or result being announced.

How does sowohl … als auch work here, and why is the verb haben after Emotionen?

sowohl … als auch is a correlative pair meaning “both … and …”. It connects two equal elements:

sowohl Medien als auch Emotionen = both media and emotions

Together they form one compound subject, so the verb comes after the second part and is conjugated in the plural:

Sowohl Medien als auch Emotionen haben Macht.

You cannot put a verb in between the two parts of the pair; the verb comes after the entire sowohl–als auch group.

Why is there no article in Sowohl Medien als auch Emotionen haben Macht?

In German, when you talk about plural nouns in a general sense, you can often omit the article:

Kinder brauchen Liebe. – Children need love.
Bücher sind teuer. – Books are expensive.

Here, Medien and Emotionen are meant generally, not specific ones, so no article is needed:

Sowohl Medien als auch Emotionen haben Macht.

You could say Die Medien und die Emotionen haben Macht, but that sounds more like you are talking about specific, identifiable groups. The version without the article is more general and abstract.

What exactly does Macht haben mean, and how is it different from mächtig sein?

Macht haben literally means “to have power”, i.e. to possess influence or control:

Medien haben Macht. – Media have power.

mächtig sein means “to be powerful/mighty”:

Medien sind mächtig. – Media are powerful.

They are close in meaning, but:

Macht haben focuses on possessing power as a kind of “thing” or resource.
mächtig sein is an adjective describing a quality.

In this sentence, Macht haben sounds a bit more neutral and “sociological” (like talking about power structures), which fits the style.

Can you explain the structure of aber wir können lernen, bewusst damit umzugehen? Why are there so many verbs?

The main clause here is:

wir können lernen – we can learn

können is the modal verb (conjugated, in 2nd position), and lernen is its infinitive, placed at the end of the main clause.

Then you have an infinitive clause introduced by a comma:

…, bewusst damit umzugehen. – to deal with it consciously.

So structurally:

aber (connector)
wir (subject)
können (finite modal verb, position 2)
lernen (infinitive at end of main clause)
, bewusst damit umzugehen (infinitive clause explaining what we can learn)

It corresponds very closely to English:
we can learn to deal with it consciously.

Why is it damit umzugehen and not something like umzugehen damit?

The base verb is mit etwas umgehen = to deal with something.

Finite form: Ich gehe mit Medien bewusst um.
(separable: umgehen → ich gehe … um)

When you replace mit Medien und Emotionen with a pronoun, you get damit = with them / with it.

In the infinitive with zu, the pattern is:

object pronoun first → damit
then the infinitive of the separable verb, with zu between prefix and stem → umzugehen (um + zu + gehen)

So:

bewusst mit Medien und Emotionen umgehen
bewusst damit umgehen
bewusst damit umzugehen (in the infinitive clause)

umzugehen damit is not idiomatic; pronouns like damit normally come before the infinitive verb group in this kind of structure.

Where does bewusst belong, and what exactly is it modifying?

bewusst is an adverb here, meaning “consciously”. It modifies umgehen (to deal with), so the idea is:

bewusst damit umgehen – to deal with it consciously

In the infinitive clause, it keeps roughly the same position:

bewusst damit umzugehen

You could also say:

mit Medien und Emotionen bewusst umgehen

but you would not normally put bewusst at the very end (… damit umgehen bewusst) — that sounds incorrect or at least very awkward in standard German. Adverbs like bewusst usually stand near the verb they modify and before the verb phrase in infinitive constructions.

Why is there a comma before aber?

In German, when aber connects two main clauses, there is always a comma:

Ich möchte gehen, aber ich bin müde.

In your sentence:

Sowohl Medien als auch Emotionen haben Macht,
aber wir können lernen, bewusst damit umzugehen.

These are two independent main clauses joined by aber, so a comma is required.

Even when aber connects just words or phrases, you typically still have a comma because it’s part of a list or contrast:

Es ist klein, aber fein.

Could I say merke ich, dass sowohl Medien als auch Emotionen Macht haben … instead of using the colon? Would that change the meaning?

Yes, you can absolutely say:

Wenn ich über all diese Themen schreibe, merke ich, dass sowohl Medien als auch Emotionen Macht haben, aber wir lernen können, bewusst damit umzugehen.

(or more neatly:
…, merke ich, dass sowohl Medien als auch Emotionen Macht haben und dass wir lernen können, bewusst damit umzugehen.)

The basic meaning is the same. The difference is stylistic:

With dass, it reads like a more typical, smoothly connected complex sentence.
With the colon, the writer “steps out” a bit and presents what follows as a kind of explicit conclusion or observation: I notice the following: …

So both are grammatically fine; the colon version is just a bit more punchy or rhetorical.