I'm also seeing this issue on an M1 MBP. I'm able to go into Disk Utility and mount my external drives from there, and I'm prompted to enter my drives encryption password. And regardless of whether I check the box to remember or not, it doesn't remember and mount them again after a reboot. Not sure of the cause here, but I'm (in my head anyway) attributing my slow Finder beachball issues to whatever is causing this issue.
JeffryZ
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