If everything works normally when the coach is plugged into shore power ( and from your post that’s what I’m assuming) then the problem must lie with the generator feed
I’m not trying to insult your intelligence here; just asking to try to help.
Here might be your first place to look for the problem.
Have you checked that your shore power plug is firmly inserted into the 30 Amp receptacle in the power bay?
I had a 22M with a full options pkg and a Automatic Transfer Switch (ATS) was not available so I would not expect you have one fitted either.
Without your shore power plugged into that receptacle you will not get any power from the Genset into the coach.
If the shore power plug is inserted check to see if the breakers on the Onan itself have tripped. Your Onan manual in the Winnebago Accordion file will show you where to check the breakers
Winnebago 2019 27PE (Sold)
Vancouver Island BC Canada