I had exactly the same issue when I downloaded the new 2022 for Mac QB (reluctant download, but had to due to 2019 no longer supporting banking/transaction downloads).   I had downloaded transactions, each was taking 4-6 seconds to save - ughh!

I tried all the above suggestions, plus upgraded OS from Big Sur to Monterey (the first recommendation by Intuit help - but it made no difference).  Called again, and after 20 mins of trying many other things, I was asked to disconnect/ re-set up my online banking  (through Edit Account / online settings) ... then signed up again.  It worked!