TEarl12,
First, please give any future posts a meaningful subject Just "Help!" is simply annoying. I've changed your subject line.
You cannot take AC 12 library parts back into 11. So, if it is essential that you keep moving back and forth between AC 11 and AC 12, then you should be doing so with only the AC 11 library. You can make a copy of the AC 11 library from school and copy it somewhere on your home system and reference it for the projects that are going back and forth.
Saving the project as a PLA is another option.
Karl
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators