What does a voltmeter show on the wire going out of the tripped breaker?
Breakers, and their snapped in connection to the breaker box buss bars, do go bad. Buss bar connections can be repaired with fine files and DeOxIt electrical contact cleaner/restorer spray. Disconnect rig from ALL power (shorepower, generator, inverter) before working on breaker box internal connections.
I have the similar issue in my 2020 Bighorn Traveller. I have power at the GFI in the bathroom, no power at the Galley Island or all other plugs with a GFI sticker inside or outside. I have an AC circuit breaker marked GFI and have reset it many times.
The GFI should be the first in series of plugs, if its wired correctly. Usually GFI plugs fail and stop working all together but possibly not in this case. If there is no output from the plug and breaker, that is an easy fix. I will dig my multimeter out and start tracing where the power stops however, logic would tell me there is another resettable breaker or GFI plug for all of these to go out. My boat has 3 GFI plugs for each system near a sink.
Well I should have waited to post until I got my meter out. The very first thing is ALL of my circuit breakers are incorrectly labelled. I will correct that this week. Now the GFI tale. I had power at the GFI in the bathroom but when I checked...no output. When I removed the plug from the wall, I turned on the correct breaker to check power with my meter and I now have power go out. I checked the connections and well...well, "to whom it may concern" as Joe Kenda would say...loose wires on the output. Somebody didn't do their job. That is about 5 electrical issues I have found on this RV where work was not done properly.