About LibreOffice

When I tried to open an EXCEL file using LibreOffice, I posted the following error:
When using Office, files can be opened normally. But Office is not stable under Zorins OS. Ask for help in finding a way to open a file with LibreOffice

                                           ZORINS OS rookie

Maybe it’s a corruption in the file you’re trying to open? I opened a sample .xlsx from here https://file-examples.com/index.php/sample-documents-download/sample-xls-download/ and it opened fine for me.
Can you try with different files?

Was the file type .xls or .xlsx?
Maybe convert it to a .csv if you still have Excel available to you.

Libre Office has come a long road for compatibility with Microsoft Office and should open excel files (.xls or xlsx) just fine, as @carmar said I had downloaded the sample file too and it opened it without any issues. May be the file itself is corrupt. Try to open it in google sheets and check if the file opens fine or not.

Google Sheets