Did you make sure that Library Manager in 12 for those projects was loading the AC 10 library (or whatever libraries were originally used in the project)?
If for some reason that does not work, save a PLA of the project from 10 and open the PLA in 12.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB