После уборки в комнате стало уютнее.

Because после always takes the genitive.

So:

• после урока = after the lesson
• после обеда = after lunch
• после уборки = after the cleaning / after tidying up

The base form is уборка, but after после it becomes уборки.

Because в комнате shows location, not movement.

With в:

• в комнате = in the room, inside the room → prepositional case
• в комнату = into the room → accusative case

Here the sentence describes what the situation was in the room, so Russian uses в комнате.

This is an impersonal construction.

Russian often uses стало + comparative/adverb to mean something like:

• it became...
• things became...
• it got...

There is no real grammatical subject here, so Russian uses the default past-tense neuter singular form стало.

Compare:

• Стало холодно. = It got cold.
• Стало темно. = It got dark.
• Стало уютнее. = It became cozier.

Not in the same way as in English.

English often needs a dummy subject:

• It became cozier in the room.

Russian does not need that kind of subject here. The sentence is simply impersonal:

• В комнате стало уютнее.

So when translating into English, you may use it, but in Russian there is no actual word corresponding to that it.

Уютнее is the comparative form of уютный / уютно.

Very roughly:

• уютный = cozy, comfortable
• уютно = cozily / cozy in feel
• уютнее = cozier / more cozy

In this sentence, уютнее works as a predicative comparative: it describes the atmosphere or feeling of the room after cleaning.

So стало уютнее literally means became cozier or got more cozy.

Both are possible, but уютнее is more natural and common here.

Russian often forms comparatives in two ways:

1. simple comparative
   • уютнее
2. analytic comparative
   • более уютно

In everyday speech, the simple comparative is usually preferred when it exists. So стало уютнее sounds very normal.

It can say that, but the nuance is a little different.

• Комната стала уютнее.
  Focuses on the room itself as the subject.

• В комнате стало уютнее.
  Focuses more on the feeling/atmosphere in the room.

• После уборки в комнате стало уютнее.
  Adds the idea that this change happened after the cleaning.

The version with в комнате стало уютнее sounds very natural when talking about how a place feels.

Because this is still just one simple sentence, not a subordinate clause.

После уборки is only a prepositional phrase meaning after the cleaning. It is not the same as a full clause like:

• После того как убрались, ... = After they cleaned up, ...

Since После уборки в комнате is just part of one simple sentence, no comma is needed.

Yes. Russian word order is flexible, and changing it changes the focus more than the basic meaning.

Possible variants:

• После уборки в комнате стало уютнее.
  Neutral: first gives the time/circumstance, then the place.

• В комнате после уборки стало уютнее.
  Slightly more focus on in the room.

• Стало уютнее в комнате после уборки.
  More marked; can sound more expressive or context-dependent.

The original order is very natural.

Уборка means cleaning or tidying up, especially in a home or room.

So после уборки can mean:

• after cleaning the room
• after tidying up
• once the cleaning was done

It does not have to refer to a professional cleaning service. It usually just means the room was cleaned/tidied.

Yes, that is a fairly literal way to understand the structure.

A more natural English translation might be something like:

• After cleaning, the room felt cozier.
• After the room was cleaned, it became cozier.
• It felt cozier in the room after cleaning.

But grammatically, the Russian structure really is close to After cleaning, in the room, it became cozier. English usually smooths that out.