3GPP 24.501 v20.0.0 — the document's own text
5.2.3.1 General
Taught in 4. Inside TS 24.501, the document at the centre (CT1 — the group that writes what your phone says, overview).
The state 5GMM-REGISTERED is entered at the UE, when the initial registration procedure is performed by the UE (see clause 5.5.1.2.2).
In state 5GMM-REGISTERED, the UE shall behave according to the substate as explained in clause 5.2.3.2.