What do you call a person that’s on break / temporarily retired?
At universities, professors will go on sabbatical:
[Merriam-Webster]
3 : a break or change from a normal routine (as of employment)
Typically, this lasts for a year, after which they return to their normal teaching duties.
In more general terms, you can also simply say that somebody is on leave:
[Merriam Webster]
1 b : authorized especially extended absence from duty or employment
However, there is no single word adjective for this that I know of. The closest expression is off duty, but that can be a regular (daily) occurrence rather than a longer absence.