Hi, Raymond -
32-bit isn't "going away" anytime soon. Your v8 to v2019 R2 migration is going to have to take on the ANSI-to-Unicode transition that occurred in PB 10. My advice is to keep your migration as simple as possible and leave it 32-bit, at least initially, and make sure it is working well before attempting to migrate to 64-bit.
I also would advise you to leave your PB applications as 32-bit UNLESS you have some requirement(s) for using 64-bit. As Mike has already mentioned, if your app uses calls to the Windows API, other external DLL's, OCX's, database interface drivers, other applications such as MS Office products, etc. there are implications for transitioning to 64-bit. Switching to 64-bit PB app's "just because" is a very poor reason to do so.
Keep in mind the PB IDE is 32-bit, so you need 32-bit versions of things the IDE works with in order to develop in PowerBuilder. The PB debugger is 32-bit, so debugging a 64-bit PB app is therefor problematic at the present time.
My last word of advice is when you are ready to take on 64-bit development in PB, start with a simple, small, application first, if possible to learn the in's & out's, then go from there. Baby steps!
Regards, John