Hello @pamela77
Thank you for reaching out to the Community regarding your issue, although I am sorry to hear that you are experiencing issues with your current computer. As far as Quicken goes on whether it's better on Catalina or Big Sur they should run similarly overall as long as you're able a solution to your hard drive you shouldn't experience any performance issues.
I do wish you luck with the computer troubles and I believe a couple of other users may have some more recommendations on what could be best.
Thanks,
Quicken Francisco