Have a look at this thread, especially the answer by @Tosche:
If you look at the end of the thread, you see that things are improving a lot in recent releases:
If you get your M1 Mac later this year, it seems like most issues will be resolved by then. For example, Glyphs now ships with Python 3.9.1, so you no longer need to download that manually.
Also note that this is mainly about plugin support. Glyphs 3 by itself runs fine on M1.