3GPP 23.501 v20.2.0 — the document's own text
D.4 Support for UE capable of simultaneously connecting to an SNPN and a PLMN
Taught in 24. Networks that are not for everybody (The 5G system architecture, in depth).
When a UE capable of simultaneously connecting to an SNPN and a PLMN and the UE is not set to operate in SNPN access mode for any of the Uu/Yt/NWu interfaces, the UE only performs PLMN selection procedures using the corresponding interface for connection to the PLMN.
A UE supporting simultaneous connectivity to an SNPN and a PLMN applies the network selection as applicable for the access and network for SNPN and PLMN respectively. Whether the UE uses SNPN or PLMN for its services is implementation dependent.
A UE supporting simultaneous connectivity to an SNPN and a PLMN applies the cell (re-)selection as applicable for the access and network for SNPN and PLMN respectively. Whether the UE uses SNPN or PLMN for its services is implementation dependent.