antspants,
Whenever you upgrade a software like office, they tell you it is backwards compatible, and i never had a problem with that. going the other way, you may run into problems because of new options that are not available in the old software. usually, you will get a popup telling you that certain things will not work because of this. The only difference i have discovered is the accessibility function. that does not make the spreadsheet unusable.
I sat down at the desktop today and opened both files and tried again if the copy-paste procedure. it works fine. i noticed that the original spreadsheet (with the 200 pages) responds slower than the one with the 20 pages. I guess that is to be expected because of the size of it.
Since both are working and the new one is faster, i will use the new one coming January 2024.
Thanks for your help