Lat som ingenting og hold masken for ikke å stoppe sceneøvelsen.

No. Here lat is a verb, not the adjective lat meaning lazy.

It is the imperative form of å late som, which means to pretend / to act as if.

So:

• lat = pretend / act as if
• adjective lat = lazy

They look the same in writing, but they are different words.

Because this is an imperative sentence, giving an instruction or command.

In Norwegian, the subject is usually left out in imperatives:

• Hold masken. = Keep a straight face.
• Kom hit. = Come here.

So in Lat som ingenting og hold masken ..., the understood subject is you.

It is a fairly natural shortened expression meaning pretend nothing happened or act like it was nothing.

A fuller version would often be something like:

• Lat som ingenting har skjedd.

That literally means Pretend as if nothing has happened.

So lat som ingenting is a more compact, idiomatic version. In speech, Norwegian often leaves out what is understood from context.

Literally, hold masken means keep the mask on.

Idiomaticly, it means something like:

• keep a straight face
• don’t show your reaction
• stay composed

So it is not usually about a real physical mask. It is a fixed expression about controlling your facial expression or emotions.

Because holde masken is a set idiomatic expression, and it normally uses the definite form:

• masken = the mask

Many idioms in Norwegian use the definite form even when English would not think of it as a specific object.

So hold masken is the natural expression, not usually hold en maske.

Because for ikke å + infinitive is a very common Norwegian pattern meaning:

• in order not to ...
• so as not to ...

So:

• for ikke å stoppe = so as not to stop

This word order is normal in Norwegian infinitive phrases with negation:

• for ikke å glemme
• for ikke å le
• for ikke å stoppe sceneøvelsen

So ikke comes before å + verb in this structure.

Yes. Here stoppe is being used transitively, meaning to stop/halt/interrupt something.

So:

• stoppe sceneøvelsen = stop the scene exercise

Norwegian stoppe can be used both ways:

• Bilen stoppet. = The car stopped.
  intransitive
• Han stoppet bilen. = He stopped the car.
  transitive

In your sentence, it is the transitive use: the speaker does not want the exercise to be interrupted.

Because Norwegian usually writes compound nouns as one word.

So:

• scene
  • øvelse = sceneøvelse

Then the definite singular ending is added:

• sceneøvelsen = the scene exercise

This is very normal in Norwegian. English often writes similar ideas as two words, but Norwegian usually combines them.

The definite form sceneøvelsen suggests a specific exercise that both speaker and listener already know about.

So it is not just any scene exercise, but the one they are currently doing or talking about.

Compare:

• en sceneøvelse = a scene exercise
• sceneøvelsen = the scene exercise

That makes sense in a context like acting class, rehearsal, or drama training.

It can be used for one person or several people.

In modern Norwegian, the imperative form is generally the same regardless of number:

• Lat ...
• Hold ...

So the sentence could be said to one person or to a group, depending on context.

Yes, that would also be natural, and it is a bit more explicit.

There is a small difference in feel:

• Lat som ingenting = shorter, more compact, more context-dependent
• Lat som om ingenting har skjedd = fuller and clearer

Both are understandable and natural, but the shorter version sounds more clipped and immediate, which can fit spoken instructions well.