Why won't Writer "Save as..." to a different file format other than ODT?

I’m on a MacBook Pro,Catalina, 10.15.6, I downloaded LibreOffice 6.4.5.2. Created a large document in Writer as ODT and it will not save to any other file format. There are other file formats available in the pop-up. I used to be able to save as other formats in older versions of LibreOffice. Did I do something wrong? Can this be fixed?

Have you provided Full Disk Access to LibreOffice.app (this procedure may be required to be repeated on updates of LibreOffice, even if there is still an existing entry)?
Have you tried to test the failing procedure while running in LibreOffice Safe Mode (Help -> Restart in Safe Mode...)?

Yes, It has Full Disk Access, I checked that. When you say repeated, what does that mean in actual keystrokes? Do I have to go into the Privacy settings, undo it, close, restart, then go into Privacy settings again, and provide Full Disk Access?

“Save as…” doesn’t even work in Safe Mode. Just tried it.

Do I have to go into the Privacy settings, undo it, close, restart, then go into Privacy settings again, and provide Full Disk Access?

Yes - exactly

Okay. Did that. Now I have more information. LIbreOffice will save a copy, export to PDF and save as DOC, but only for a little while on a small document. If I try on a larger document, like 50 pages, it crashes. If I shut down and turn on again, it behaves okay for a little while, then when I try to save a large copy, or save as . . ., it crashes. Is this a memory problem of some kind?