For anyone else that comes across this. The behavior as I now understand it is (using UE5):
(1) You should establish your source control setup prior to attempting to do Multi-User Editing
(2) If you previously have installed your source control engine software (Perforce, GIT Command line) then UE will attempt to access those commands. A failure here could be due to installation error, commands not in global PATH, or possibly other errors.
(3) When entering Multi-User Editing, Source Control will be replaced by “Multi-User”, but the original source control engine details will be visible below this.
(4) All source change operations (while on Multi-User) will be cached on the Host(?) computer. When the session ends, the Host user will be prompted to save cached changes. This will queue the changes in source control.
(5) There is a way to have changes immediately save for source control Persist Change(?), however, I’ve been unable to find where this setting is in UE5. It’s possible this only works with Perforce, but I’m on Mac and can’t test this. GIT is usually a two-stage local and then server push, so it’s unclear if it’s even possible for Unreal to manage both of those steps automatically. I usually have to manage this on the command line.
(6) Unreal will also auto-checkout files if you enable this option under the Multi-User settings. I didn’t test this and this likely suffers the same source control challenges from #5.