Safari 15.1 not responding

Since updating to 15.1 two days ago, Safari is becoming unresponsive 4 or 5 times a day, so I have to Force Quit. I've already disabled my only extension (1Blocker) and cleared all cookies and cache.

This is on an M1 Air running 11.6.1 and it's the first fault of any kind I've encountered in 10 months of ownership. Apple telephone support just said "upgrade to Monterey first, then we'll help".