Anyone else seeing horrible performance / unusable system after updating to Sequoia?

Updated to Sequoia today (RC), and my Mac is essentially unusable since. iCloud syncing takes ages (say I delete a reminder on my iPhone, it finally deletes on my Mac in 30 minutes or so), Mail similarly takes 30-60 minutes to sync changes to the server. Spotlight is unusable (won't return results), apps hang on launch and take 1-2 minutes to finally open, apps take 1-2 minutes to quit after CMD-Q, and I can't even get into my Mac - after entering my correct password at the lock screen, I sit for probably 2-3 minutes before the Desktop finally shows.

System was perfectly fine this morning before the update. Has anyone else seen this and discovered a cause?