Safari 14.0 loads pages impossibly slowly

On my main account, Safari 14.0 (OS10.15.7) loads pages impossibly slow. Not merely sluggish-- like 100X-1000x too slow, perhaps 20-30 minutes to load a page that used to take a few seconds. There is NO such problem under my test account, nor does Chrome have a problem. I'm not sure, but Safari seems to be running ok except for the page loading issue-- it's a little hard to tell, since most of the time, it's bogged down loading a page. Page loading also affects the performance of all other functions running concurrently, including Activity Monitor, and Finder, which tend to hang for tens of seconds at a time while a Safari load is going on. I've cleared cache, history, cookies, removed all Safari extensions, and disabled anti-virus; no help. Activity Monitor does NOT show Safari or any other functions running at very high CPU usage or consuming huge amounts of memory!!! I've been searching the internet for a month or more looking for a solution, and i've tried all the normal remedies, with no luck. I've switched to Chrome for now, but I hate losing the integration with iCloud, so I'd like to get Safari back. I'm willing to reinstall whatever needs to be reinstalled, if there's a good chance that will help.