Bei so vielen Aufgaben verliere ich leicht den Überblick.

Here bei means something like when faced with, with, or in the case of.

So bei so vielen Aufgaben does not literally mean physical location like at or by. Instead, it sets the situation:

• Bei so vielen Aufgaben = with so many tasks
• more naturally in English: when there are so many tasks / faced with so many tasks

This use of bei is very common in German when describing the circumstances in which something happens.

Examples:

• Bei schlechtem Wetter bleiben wir zu Hause.
  = In bad weather / When the weather is bad, we stay home.
• Bei so viel Lärm kann ich nicht arbeiten.
  = With so much noise, I can’t work.

Because bei always takes the dative case, and Aufgaben is plural.

So the phrase changes like this:

• nominative/accusative plural: so viele Aufgaben
• dative plural: so vielen Aufgaben

That is why you get:

• bei so vielen Aufgaben

Also notice that plural dative nouns usually add -n if possible:

• die Aufgaben → den Aufgaben in regular dative plural contexts

Here the adjective also gets the dative plural ending:

• viele → vielen

This is a dative plural noun phrase:

• so = intensifier, meaning so
• vielen = form of viel used here like an adjective, in dative plural
• Aufgaben = plural noun, tasks

So the structure is:

• bei
  • dative phrase
• bei so vielen Aufgaben

You can think of so vielen as meaning so many.

Compare:

• so viele Aufgaben = so many tasks
• bei so vielen Aufgaben = with so many tasks

Because German main clauses follow the verb-second rule.

The first position in the sentence can be taken by different elements, not just the subject. Here, the sentence begins with the prepositional phrase:

• Bei so vielen Aufgaben = position 1

Then the conjugated verb must come next:

• verliere = position 2

Then comes the subject:

• ich

So the structure is:

• Bei so vielen Aufgaben | verliere | ich | leicht den Überblick

If you started with the subject instead, you could also say:

• Ich verliere bei so vielen Aufgaben leicht den Überblick.

That is also correct.

Because verlieren is a transitive verb and takes a direct object in the accusative.

Here:

• ich = subject
• verliere = verb
• den Überblick = direct object

So:

• der Überblick = nominative
• den Überblick = accusative masculine

This is exactly like:

• Ich verliere den Schlüssel.
  = I lose the key.

In your sentence:

• Ich verliere den Überblick.
  literally = I lose the overview
• idiomatically = I lose track / I get overwhelmed / I can’t keep everything straight

Yes, it is a very common expression.

Literally:

• den Überblick verlieren = to lose the overview

But in natural English it usually means:

• to lose track
• to lose sight of what’s going on
• to get overwhelmed by too much information or too many things to manage

So in this sentence, the speaker is saying that with so many tasks, they easily stop being able to keep track of everything.

Related expression:

• den Überblick behalten = to keep track / to stay on top of things

Example:

• Bei all den Terminen ist es schwer, den Überblick zu behalten.
  = With all those appointments, it’s hard to keep track of everything.

No. Here leicht means easily.

That is a very common use of leicht as an adverb.

So:

• ich verliere leicht den Überblick = I easily lose track

Compare:

• Das ist leicht. = That is easy.
  Here leicht is an adjective.
• Ich vergesse Namen leicht. = I easily forget names.
  Here leicht is an adverb.

German often uses the same form for adjective and adverb, unlike English.

Yes, adverbs like leicht can move around somewhat, though some positions sound more natural than others.

Your sentence:

• Bei so vielen Aufgaben verliere ich leicht den Überblick.

Also possible:

• Ich verliere bei so vielen Aufgaben leicht den Überblick.
• Ich verliere leicht den Überblick bei so vielen Aufgaben.

All are understandable, but the original sounds very natural because it first sets the situation, then gives the result.

In general, leicht often appears before the part it modifies most directly, here the verbal idea den Überblick verlieren.

Yes, mit so vielen Aufgaben is possible, but it is not exactly the same in feel.

• Bei so vielen Aufgaben emphasizes the situation/circumstances:
  when there are so many tasks
• Mit so vielen Aufgaben can sound more like having/dealing with so many tasks

Both can work, but bei is especially natural in this kind of general statement.

Compare:

• Bei so vielen Aufgaben verliere ich leicht den Überblick.
• Mit so vielen Aufgaben verliere ich leicht den Überblick.

The first is slightly more idiomatic for many speakers.

Because so viele already works as a determiner-like quantity expression: so many.

So German does not need an article here.

Compare:

• so viele Aufgaben = so many tasks
• die Aufgaben = the tasks

You normally would not say:

• bei so vielen den Aufgaben ❌

That would be incorrect.

Aufgaben can mean several related things depending on context:

• tasks
• assignments
• duties
• exercises (especially schoolwork)

In this sentence, it most naturally means tasks or things to do.

So the sentence could describe:

• work responsibilities
• homework
• chores
• general obligations

Yes, but the meaning changes slightly.

• leicht = easily
  Focus: it happens without much difficulty; the speaker is prone to it.
• schnell = quickly
  Focus: it happens fast.

So:

• Ich verliere leicht den Überblick.
  = I easily lose track.
• Ich verliere schnell den Überblick.
  = I lose track quickly.

Sometimes both are possible, but they are not identical.

It is neutral, standard German.

It works well in:

• everyday conversation
• writing
• workplace situations
• school/university contexts

It is neither slangy nor especially formal.

A more casual English-style equivalent might be:

• I get overwhelmed with so many tasks.
• I lose track when I have so much to do.

But the German sentence itself is perfectly normal and natural in most contexts.