After reinstalling Win 10 - which is another story- I installed LO7.5.
Almost immediately I discovered that it would hang for 1 or 2 minutes, “not responding” before loading my Budget spreadsheet of 4 sheets.
After hours of searching the web for clues and trial and error I found that LO7.5 would satisfactorily load and save Write and Impress files and also old Calc files that had not been saved by LO7.5-Calc.
I reverted to LO7.4 but it still would not load my budget spreadsheet. I solved my problem by creating a new blank SS and pasting my budget sheets to it.
While searching for a solution I found in Event Viewer app a “cross process” error listed for an attempt to open the file.