Problem solved. Updated the M1XEP to 2.0.51. Did not have to try anything else. Turned on update checking each time ElkRP2 is started to remind me to update.

During my research, as Guy noted, there is a lot of information available about Google restricting 3rd party apps from accessing Gmail starting in summer 2024. Sooner or later I expect this may end up impacting M1 owners using Gmail for text messaging.

Thanks Brad and Guy!