You are in the situation of owning the house, but using the wrong key will not open the door. So you have to find out, what has happened (as you had this key earlier…).
I assume you have saved files during this time.
Where did you save? Anything special there? NAS, Cloud storage, SMB-share… Can you “see” your files in the file-manager of your (I guess) ZorinOS?
Is the folder below your home-folder?
This may be rights of the “location”, so not the right for a file, but for the folder. To create a file you need the right to modify the folder.
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Wild guess: Your LibreOffice is in a Flatpack and on update lost the right to write to write to the folder you want to use…
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A solution depends on the situation. A Flatpack needs something like Flatseal to edit rights, rights for files and folders can be changed directly or on command-line …
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PS: You are always logged in under the same name? No root/admin-account used?