I just installed BIAB/RB 2021 from 2019. However, it looks like RB didn't update the old 2019, so I have RealBand.exe, which is 2019 version, and RealBand64.exe, which is 2021. Is there any reason to keep both?
yes, for one, you'll need to re-add all your plugins to RB 2021 because if you open a 32 bit file in the 64 bit version you'll lose all your plugins and plugin settings. i did a screenshot of the vsts i'd added in 32 bit RB and added them again in the 64 bit version.. second, the 64 bit PG Music plugins don't as yet come with the usual presets so if you want to load them with presets you are used to in new projects (not sure if settings carry over on files saved originally in 32 bit)either do it in 32 bit or copy the preset from the 32 bit to the 64 bit version. again i've used a screenshot of the plugin i use most - the BIAB default reverb that gets lost when you open a BIAB file in RB.
You should install this patch:
https://dl14.pgmusic.com/support/patch/realband_2021_update_build3c.exeThis (1) updates the 64-bit plugins so that the presets are available, and (2) allows you to run the latest 32-bit version (RealBand.exe 2020) if need be)
After applying the patch, can I then get rid of BIAB 2019? I don't understand why I need to keep the 2-year old version of the software after I've upgraded.
If you installed the patch, you should have and be able to run the 2020 build 5 realband.exe, which is the latest 32-bit version. No, I can't think of a reason why you would need 2019.