Det sägs att hon ska börja ett nytt jobb i höst.

Det is a dummy subject here. It does not refer to a specific thing; it is just required to make the sentence work grammatically.

Det sägs att ... is a very common Swedish way to say:

• It is said that ...
• People say that ...
• It is being said that ...

So in this sentence, det is not really it in the concrete English sense. It is more like the formal subject in expressions about weather, time, or general statements.

Sägs is the passive form of säga in the present tense.

• säger = says / are saying
• sägs = is said / are said

Swedish often forms the passive by adding -s to the verb.

So:

• Det sägs att ... = It is said that ...
• Man säger att ... = People say that ...

Both are possible, but det sägs sounds a bit more impersonal and report-like.

They are very close, but not exactly identical in tone.

• Det sägs att ... = It is said that ...
  • more impersonal
  • often sounds a bit more formal, detached, or like hearsay
• Man säger att ... = People say that ...
  • more direct
  • still general, but slightly less impersonal

In many situations, either one would work. In this sentence, det sägs fits well because the speaker is passing on information without naming a source.

Here ska börja means something like is going to start or is supposed to start.

Ska often expresses:

• future
• intention
• plan
• expectation

So hon ska börja ett nytt jobb i höst suggests that starting the new job is planned or expected.

It is not a pure future marker in every case. Swedish does not have one single future tense like English sometimes seems to. Instead, Swedish often uses:

• ska
• kommer att
• the present tense

Each can give a slightly different feeling.

Both are possible, but the nuance is a little different.

• ska börja often suggests a plan, arrangement, or expectation
• kommer att börja often sounds more like a neutral prediction about the future

So:

• Hon ska börja ett nytt jobb i höst = she is going to start a new job this autumn / she is set to start
• Hon kommer att börja ett nytt jobb i höst = she will start a new job this autumn

In this sentence, ska sounds natural because it is about a planned life event.

Because jobb is an ett-word in Swedish:

• ett jobb = a job

Adjectives must agree with the noun, so:

• en ny bil
• ett nytt jobb

The adjective ny changes to nytt with an ett-word in the singular indefinite form.

So:

• ny = common gender singular
• nytt = neuter singular
• nya = plural or definite

I höst is the normal idiomatic way to mean this coming autumn / in the autumn when talking about a future time period.

So:

• i höst = this autumn / in autumn
• i vinter = this winter
• i sommar = this summer

På hösten usually means in the autumn season in general, often as a recurring or habitual time.

Compare:

• Hon ska börja ett nytt jobb i höst. = She will start a new job this autumn.
• På hösten blir det ofta kallt. = In autumn, it often gets cold.

Because after att, Swedish uses normal subordinate clause word order.

In the clause:

• att hon ska börja ett nytt jobb i höst

the order is:

• att
  • subject + verb

So:

• att hon ska börja ...

This is standard. You do not invert the subject and verb after att.

Compare:

• Main clause: Hon ska börja ett nytt jobb i höst.
• Subordinate clause: ... att hon ska börja ett nytt jobb i höst.

The word order stays subject-first here.

Yes, that is also possible in Swedish.

Swedish very often uses the present tense to talk about the future when the time is clear.

So all of these can be possible:

• Hon börjar ett nytt jobb i höst.
• Hon ska börja ett nytt jobb i höst.
• Hon kommer att börja ett nytt jobb i höst.

The differences are mainly in nuance:

• börjar = neutral, often natural when a future time is already stated
• ska börja = more sense of plan or arrangement
• kommer att börja = more explicitly future, sometimes more predictive

Yes, it suggests that the speaker is reporting hearsay rather than stating a confirmed fact.

It gives the feeling:

• this is what people are saying
• I have heard this
• I am not necessarily the direct source

So the sentence is useful when you want to sound cautious or when the information is not being presented as personally verified.

Yes, very often. It is a common pattern in Swedish.

For example:

• Det sägs att han är rik. = It is said that he is rich.
• Det sägs att de ska flytta. = It is said that they are going to move.
• Det sägs att restaurangen är väldigt bra. = People say the restaurant is very good.

It is a useful structure for reporting rumors, public opinion, or second-hand information in an impersonal way.