What 'APPLE BIT' changes are you referring to?
Do you mean the switch from 32-bit to 64-bit software which, as noted, happened some 20 yeas ago, and mandated for the past 5 years.
And what version of Reunion are you using.
According to https://www.leisterpro.com/doc/v14/questions/answers/mymac.php :
Reunion 14 is a 64-bit app and is compatible with both Apple Silicon Macs (using Apple's new M1, M2, M3 or M4 chip) and Intel chips.
Given that, it sounds like 64-bit isn't the problem, unless you're using an old PowerPC-based Mac, or a system that doesn't support 64-bit applications? If so, that's not entirely Apple's fault. Just because the genealogy software can track back your family over hundreds of years, that doesn't mean it requires equally-old hardware to run on.
Besides, if your hardware and your OS only supports 32-bit applications, there's nothing stopping you continuing to use that. The old Reunion software should still work, you just won't be able to run the latest versions of everything.