I have started this new thread because my previous one was closed! I just wanted to thank
@Greg_the_Geek for his help with this problem. I took his suggestion of creating a new Windows 11 profile and that seems to have fixed the problem! I can now Open and Save the datafile without crashing. Performance for Open even seems to be noticeably better.
Unfortunately, the new account is causing new headaches mainly because of OneDrive, which I am not quite able to grasp yet, but which I expect to be able to work thru in the next few days.
Again, wanted to thank you for putting time into, and ultimately solving my problem. Sadly, it was more than Support was able to accomplish other than to identify a "memory leak" problem.