I am currently seeing EXACTLY the same behavior described back in 2023 on an earlier release:
Reverting to R63.19 did not solve this. Reverting to R62.16 did however.
In another data file I was seeing different behavior - doing a One Step Update All Accounts (which on the initial go around only ever updates online quotes - long running defect that I just ignore by doing it a second time and re-check all accounts) that update was also spinning forever and Quicken had to be killed/restarted. Reverting to 62.16 also solved this issue for me.
I too had to revert back to R62.16 on 2 computers. Wonder when R63.21 will be ready for prime time?
I accidentally re-upgraded to R63.21 without thinking about it. After the re-upgrade the issue has gone away. Kinda screwy.