3GPP 23.501 v20.2.0 — the document's own text
5.32.7.1 General
Taught in 11. Using two accesses at once (The 5G system architecture, in depth).
Multi-access connectivity using ATSSS established via EPC only is not supported.
Interworking for MA PDU Session, if allowed by the network, is based on the interworking functionality specified in clause 5.17.2, with the differences and clarifications described in the following clauses.
A PDN Connection in EPS may be modified into a MA PDU Session when transferred to 5GS if the UE and the SMF+PGW-C support the ATSSS feature.