As mostly people report their problems here, I just wanted to share my very positive opinion:
After waiting veeeery long (never change a running system) I just updated my complete setup: New Mac, new OS (but I stay on 10.14.6 for now), new Database-Version and GarageSale 8.2 Pro (from GS7).
And what should I say? It simply works perfect. GS 8.2 seems to be smoother that 7 was, the transfer of thousands of listings worked fast and without any glitch. There was just one small minor optical issue, I will open another thread for that. All my AppleScripts work. Great! Seems to be something that may work for the next years again.
Thanks for the iwascoding-team for their effort in working on GarageSale!