Hi, @musicgal, yes your 75-300 EF lens will work fine for a fullframe camera. That’s what it’s made for! (So when you use it on a crop sensor you get more reach, which is handy.)
See here for more details: https://community.usa.canon.com/t5/EF-RF-Lenses/What-is-the-difference-between-EF-and-EF-S-lenses-and-what-is/td-p/139263
Summary, in case the link goes dead in the future:
EF lenses work on both types of Canon DSLR; full frame and crop sensor cameras. Some are affordable and some are very expensive.
EF-S lenses only work on crop sensor cameras, and are consumer grade, affordable lenses.