Performing an upgrade would not remove any existing RealTracks or RealDrums, it would only add newer ones.

Where was BiaB installed previously? That is where the original Drums and RealTracks will be located.

Installing 2021 to a different drive will likely place the newer RealTracks / RealDrums on the new drive and leave the existing ones on the old drive. Cannot do this.

It seems from above that you have already done this, but in case, if they are now split across 2 drives, you can either move the original files from the original drive to the new install location, maintaining the folder structure, or move the RealTracks and Drums folder from the new location to the original drive, again maintaining the folder structure. If you use the second method, you need to point BiaB to the new RealTracks and Drums folder locations (Options > Preferences) as explained previously.

If you have the Pro Pak, then this is the most basic entry level Pak available, despite the misleading name. In fact, Mega Pak has more than Pro Pak.

Can you name something that is missing that you believe that you should have?

BIAB & RB2025 Win.(Audiophile), Sonar Platinum, Cakewalk by Bandlab, Izotope Prod.Bundle, Roland RD-1000, Synthogy Ivory, Kontakt, Focusrite 18i20, KetronSD2, NS40M Monitors, Pioneer Active Monitors, AKG K271 Studio H'phones