Ich muss lange scrollen, weil in der Cloud noch viele alte Dateien gespeichert sind.

Because the subject is ich, so the modal verb müssen has to be conjugated in the 1st person singular:

• ich muss
• du musst
• er/sie/es muss
• wir müssen

So Ich muss lange scrollen means I have to scroll for a long time.

Because müssen is a modal verb. In German, when you use a modal verb with another verb:

• the conjugated modal verb goes in the normal verb position
• the main verb stays in the infinitive at the end of the clause

So:

• Ich muss scrollen.
• Ich muss lange scrollen.

That is the normal pattern.

Here lange is an adverb, not an adjective. It means something like:

• for a long time
• quite a while
• sometimes more loosely a long way down

In this sentence, it means the speaker has to keep scrolling for quite a while before reaching what they want.

Yes. scrollen is a common borrowed verb in modern German, especially in tech and everyday speech.

It behaves like a normal weak verb:

• ich scrolle
• du scrollst
• wir scrollen
• past participle: gescrollt

So scrollen is completely normal in this kind of sentence.

Because weil introduces a subordinate clause, and in German subordinate clauses are separated by a comma.

So:

• Ich muss lange scrollen, weil ...

That comma is required in standard German.

Because weil is a subordinating conjunction. In a subordinate clause, the finite verb normally goes to the end.

Main clause:

• Viele alte Dateien sind noch in der Cloud gespeichert.

Subordinate clause after weil:

• ..., weil noch viele alte Dateien in der Cloud gespeichert sind.

So the verb sind moves to the end of the clause.

German word order is more flexible than English. In a subordinate clause, the verb still goes at the end, but other elements can move around before it.

So these are both possible:

• ..., weil in der Cloud noch viele alte Dateien gespeichert sind.
• ..., weil noch viele alte Dateien in der Cloud gespeichert sind.

Both are grammatical. Starting with in der Cloud gives a bit more emphasis to the location.

Because in is a two-way preposition:

• in + dative for location
• in + accusative for direction/movement into

Here the files are already located there, so German uses the dative:

• in der Cloud = in the cloud

If there were movement into the cloud, you would use accusative:

• Die Dateien werden in die Cloud hochgeladen.

Also, Cloud is feminine in German:

• die Cloud
• dative singular: der Cloud

Here noch means still.

So the idea is:

• there are still many old files stored in the cloud

It suggests that those files remain there and have not been deleted yet.

Depending on context, noch can also mean other things, like another, yet, or in addition, but here still is the best fit.

This phrase breaks down like this:

• viele = many
• alte = old
• Dateien = files

Dateien is plural, and alte is the adjective modifying it. The adjective ending -e is the correct plural nominative ending here in this kind of phrase.

So:

• viele alte Dateien = many old files

A learner often notices that adjective endings change in German, and this is one of those cases.

Because Datei is a feminine noun, and its plural is irregular in the sense that it changes to:

• singular: die Datei
• plural: die Dateien

So the sentence uses Dateien because it means files, not file.

Both word orders are related, but the clause structure matters.

In a normal main clause, you would often say:

• Viele alte Dateien sind in der Cloud gespeichert.

In the weil clause, the finite verb goes to the end, so the verbal expression appears there as:

• ..., weil in der Cloud noch viele alte Dateien gespeichert sind.

So gespeichert sind here means are stored.

Grammatically, this is describing a state: the files are stored in the cloud. It is not focusing on the action of storing them, but on the result/state.

Because the subject is viele alte Dateien, which is plural.

• die Datei → singular → ist
• die Dateien → plural → sind

So:

• Die Datei ist gespeichert.
• Die Dateien sind gespeichert.

Since the sentence talks about many old files, German uses sind.