To update this thread:
Re: the 10x slowdown I was seeing in FMS19, the root cause has been found and there are several workarounds: FMS19.6.3 poor performance on M1 mini / Ventura - #31 by xochi
Re: updating to FMS20:
- I updated two servers (M1 Minis) from FMS19.6.3 on Ventura 13.6.3
- I first updated FMS to 20.3.1 and ran tests
- then I updated macOS to Sonoma 14.2.1
Both servers updated to 20.3.1 perfectly, and one updated to Sonoma without trouble.
However, when I updated the second server to Sonoma, it appears as if the 'fmserver' user was lost, which resulted in a variety of problems. The solution was to re-install FMS 20.3.1 a second time, and then manually update the file permissions in a few places (external backup folder, plugin files, etc.)