3GPP 24.501 v20.0.0 — the document's own text
8.2.12.2 Unavailability information
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The UE may include this IE when an event is triggered in the UE that would make the UE unavailable for a certain period and the use of unavailability period is not due to NR satellite access discontinuous coverage.