Hi, Aron -
Appeon has done a good job in resolving the many issues they inherited from SAP's muddled foray into 64-bit in PB v12.6. However, upgrading deployment bitness is not always a trivial task. It really depends on the application.
Does you legacy app utilize any Windows API calls or interface with third-party DLL's via external function declarations? There are some subtle changes concerning 64-bit: Arguments which are Windows handles are eight bytes long instead of four and this can effect the in-memory size and affect member padding within Windows API structures. Having helped several Community members with issues related to this, I can attest these can be (not always) difficult to identify. Not all API functions are affected, however.
You'll need 64-bit versions of any third-party DLL's your app interfaces with.
It sounds like you are aware of bitness-related implications on database drivers and Active-X usage. Does your app use MAPI to interface with email? Does it interface with any of the MS Office products? Rich Text?
Of course, the PB IDE and debugger are 32-bit, so you will continue to develop, debug and run the app from within the IDE as 32-bit. 64-bit only comes into play when the app is compiled/deployed. Debugging of issues that appear only in 64-bit can be difficult.
In case you have not seen it, here is a link to an overview of 64-bit deployment concerns:
https://docs.appeon.com/pb2019r3/application_techniques/ch09s03.html#Deploying_64bit
Good luck!
Regards, John