Mi piacerebbe un lavoro che non richieda troppo straordinario la sera.

It comes from piacere, which works differently from to like in English.

• piacere is closer to to be pleasing
• so mi means to me
• piacerebbe means would be pleasing

So Mi piacerebbe un lavoro... is literally something like:

• A job ... would be pleasing to me

That is why mi is there: it marks the person who would like the thing.

Italian can leave that idea implicit.

So Mi piacerebbe un lavoro che... is a natural shortened way of saying something like:

• Mi piacerebbe avere un lavoro che...
• Mi piacerebbe trovare un lavoro che...

In English, we often need I’d like to have/find a job..., but Italian can simply present the noun phrase as the thing that would be pleasing.

Piacerebbe is the conditional, and it gives the idea of a wish, preference, or something hypothetical.

• Mi piace = I like
• Mi piacerebbe = I would like

So here the speaker is not saying they already like a particular job. They are expressing a desire for the kind of job they would want.

Because this is a typical case for the subjunctive.

The speaker wants:

• un lavoro = a job

But this job is not specific or known yet. It is desired, imagined, or hypothetical. After an indefinite noun plus a relative clause in this kind of context, Italian often uses the subjunctive:

• un lavoro che non richieda...

This gives the sense of:

• a job that would not require...
• a job with the quality of not requiring...

Sometimes yes, but it changes the feel.

• richieda is the more natural choice here because the job is unspecified and desired.
• richiede would sound more factual, as if you were talking about a known or real job.

So:

• un lavoro che non richieda... = a job I’d like, of the type that doesn’t require...
• un lavoro che non richiede... = a job that, as a factual description, doesn’t require...

In this sentence, the subjunctive is the safer and more idiomatic choice.

The subject is un lavoro.

So the structure is:

• un lavoro
• che = that/which
• non richieda = does not require / would not require

In other words:

• a job that does not require...

The relative pronoun che connects the clause back to un lavoro.

Here straordinario means overtime.

This is a very common work-related meaning. So:

• fare straordinario = to do overtime
• richiedere straordinario = to require overtime

It does not mean extraordinary here, even though the English words look related.

Because here it is being used as a kind of mass noun, like overtime in English.

• troppo straordinario = too much overtime

Italian can also use the plural:

• troppi straordinari = too many overtime shifts / overtime instances

So the difference is roughly:

• troppo straordinario = too much overtime in general
• troppi straordinari = too many separate overtime periods

Both are possible, but the singular works well when speaking generally.

Because after troppo with a mass noun, Italian normally does not use an article.

Compare:

• troppo lavoro
• troppa pazienza
• troppo straordinario

This is just like saying:

• too much work
• too much patience
• too much overtime

If you made it plural and countable, you would say:

• troppi straordinari

La sera means in the evening or in the evenings, depending on context.

Italian often uses the definite article with parts of the day:

• la mattina
• il pomeriggio
• la sera

So la sera is a normal time expression.

Here it means that the overtime is in the evening. A similar alternative is di sera, but la sera is very common and natural.

It modifies straordinario.

So:

• troppo straordinario = too much overtime

The sentence does not mean doesn’t require too much in a vague general sense. It specifically means the job should not require too much overtime.

Yes, it is understandable and natural. But there are a few slightly more explicit alternatives that are also common:

• Mi piacerebbe avere un lavoro che non richieda troppo straordinario la sera.
• Vorrei un lavoro che non richieda troppo straordinario la sera.

You could also hear versions such as:

• ...che non richieda troppi straordinari la sera
• ...che non richieda straordinari serali troppo spesso

The original sentence is fine; these are just stylistic alternatives.