Jag måste fundera på om jag vill jobba hemifrån.

Because måste is a modal verb in Swedish, and modal verbs are followed directly by the infinitive without att.

So:

• Jag måste fundera = I must think / I have to think
• not Jag måste att fundera

Other common modal verbs work the same way:

• Jag kan jobba = I can work
• Jag vill jobba = I want to work
• Jag ska jobba = I will/am going to work

So in this sentence, måste fundera is completely normal.

Because fundera på is a very common Swedish expression meaning to think about, to consider, or to reflect on something.

• fundera by itself = reflect / ponder
• fundera på något = think about something

In your sentence:

• Jag måste fundera på om ...
  literally: I have to think about whether ...

The på belongs to the expression. English learners often want to leave it out, but in Swedish it sounds natural to keep it here.

Here, om means whether (or sometimes if in English).

It introduces an embedded yes/no question:

• om jag vill jobba hemifrån = whether I want to work from home

Compare:

• Jag vet inte om han kommer. = I don’t know whether he’s coming.
• Hon frågade om jag var trött. = She asked whether I was tired.

So this om does not mean about here. It means whether/if.

Because the part after om is a new clause, and that clause needs its own subject.

Breakdown:

• Jag måste fundera på = I have to think about
• om jag vill jobba hemifrån = whether I want to work from home

Even though English also repeats I here, learners sometimes expect Swedish to leave it out. But it cannot be omitted in this sentence. The second jag is required because om jag vill jobba hemifrån is a full subordinate clause.

For the same reason as with måste: vill is also followed by an infinitive without att.

So:

• jag vill jobba = I want to work
• not jag vill att jobba

Be careful: Swedish vill + infinitive is different from English want to.

• English: I want to work
• Swedish: Jag vill jobba

No separate word for to is needed there.

Hemifrån means from home.

In the phrase:

• jobba hemifrån = work from home

This is the normal Swedish way to say it.

A useful comparison:

• hemma = at home
• hemifrån = from home
• hem = home / to home (in some contexts)

So:

• Jag är hemma. = I am at home.
• Jag jobbar hemifrån. = I work from home.

Even though English says work from home, Swedish often uses hemifrån as one word.

Yes. Both are correct, but they differ a bit in style.

• jobba = work, common and everyday
• arbeta = work, slightly more formal or neutral

So both of these are fine:

• Jag måste fundera på om jag vill jobba hemifrån.
• Jag måste fundera på om jag vill arbeta hemifrån.

In everyday spoken Swedish, jobba is very common.

The finite verbs are in the present tense:

• måste = must / have to
• vill = want

But notice that this does not necessarily mean the action is happening right now in a literal present-time sense. In Swedish, just like in English, present forms can express a current situation, decision, or obligation.

So:

• Jag måste fundera på ... = I need to think about ...
• jag vill jobba ... = I want to work ...

The infinitive fundera and jobba are not tense-marked themselves.

The sentence has two parts:

1. Jag måste fundera på
2. om jag vill jobba hemifrån

In the main clause, Swedish normally follows V2 word order: the finite verb comes in the second position.

• Jag (first position)
• måste (second position)

In the subordinate clause after om, the word order is different:

• om jag vill jobba hemifrån
• subject jag comes before the verb vill

That is normal Swedish subordinate-clause word order.

So this sentence is a good example of:

• main clause: Jag måste ...
• subordinate clause: om jag vill ...

Yes, very common.

It is often used when someone is considering a question or decision:

• Jag funderar på om jag ska flytta. = I’m thinking about whether I should move.
• Hon funderar på om hon vill följa med. = She’s thinking about whether she wants to come along.

So fundera på om ... is a useful pattern to learn as a chunk:

• fundera på om + clause
  = think about whether + clause

Yes, it sounds natural and idiomatic.

A native speaker would understand it immediately as something like:

• I need to think about whether I want to work from home.

You could also hear close alternatives such as:

• Jag behöver fundera på om jag vill jobba hemifrån.
• Jag måste tänka på om jag vill jobba hemifrån.

But your original sentence is perfectly natural, and fundera på is especially good for the idea of considering a decision.