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LibreOffice is working great and is compatible. I have never had any issues with formulas. I suppose if there are some very complex macros or formulas then it will break, but then you are probably using the wrong tool anyway.

> most use it for compatibility sake

Which kind of is on Microsoft for not fixing the situation and just carrying cruft every release. They could have a separate tool to fix/migrate to whatever modern format they are using nowadays (or to some "light" format that doesn't allow all the features 99% of users don't care about).

Their subscription could be much cheaper.

It goes beyond the file formats. There is an entire ecosystem of industry specific extensions and plugins that are heavily used in law and accounting firms. These only work with MS office and they are critical to how many businesses operate.