2021.3.20f1 constantly beachballs on "Reload Script Assemblies"

Even on a very simple project with few assets and packages, the current LTS version beachballs on my iMac pretty much constantly whenever it gets to the “Reload Script Assemblies” step after compile. I’d say 8 out of 10 times - making the editor all but unusable. The rest of the system remains usable, so it’s not a general system freeze. It’s also not a problem with scripts or assets - after force-quitting and reloading, it happily runs the game (until the next time it compiles something).

Who slept during QA?
How can I help to debug/fix this? The Bug Reporter never shows up, so the editor itself doesn’t ever register this as an issue.

More details: After several minutes(!!) it eventually works itself out, at least sometimes. I can launch other apps and work in them while it’s beachballing, again pointing to this not being a system problem. The MacOS activity monitor shows no CPU use or other noticeable activity from Unity during this time, so what the heck is it doing?

I’m running MacOS Mojave 10.14.6, 16 GB of RAM, plenty of disk space available.

I’m also pretty sure it’s a problem recently introduced - I have an older project on 2021.3.16 that works just fine.

After some more tries with multiple projects: Consistent issue, not reliably reproducable but happens very often. Really makes it hard to work. Getting frustrated with Unity these days.

Bug report through the in-editor bug report is sent. Still wondering how this got through QA or if I’m the only person having this problem.