I don’t know, Apple releases a “new” version of macOS with big fanfare every year, and I’ve never heard anyone complain about it as if it were a huge breaking change.

Linux supports it, but (some?) motherboards won’t boot without a display connected. I had this issue recently when I converted my old PC to a NAS and I had to buy a dummy plug.

You won’t be using a traditional RAID with TrueNAS Scale. You have a choice of Stripe, Mirror, RAIDZ1, RAIDZ2, RAIDZ3, dRAID1, dRAID2, dRAID3. The docs are very detailed, so you should read up on RAIDZ and the other types elsewhere, too.