Do NOT tell anybody in the office that you use Libre Office.
If you do, you will be blamed for every problem anyone encounters.

Font size looks incorrect - Carl’s fault for using libre office to edit the file (even though you never worked on that project at all).

Paper jamb in the printer - Carl’s fault for printing a document from that weird libre office program.

I got fired for saying something racist on twitter - Carl’s fault for using that weirdo libre shit.

I don’t. I just export to PDF if I need them to see formatting the same.

Does this actually cause compatibility issues? If not, no need to explain

I don’t owe my co-workers any explanation.

Literally no one will care. Just make sure that your documents works well for them.

You don’t. Enjoy better, faster and more effective software and laugh when their shot breaks.

The better question asked is:

How do they explain to you that they don’t?

If the colleague is provoking you, a dismissal answer could be a good call, like (hypothetical case) “you use iPhone and I use Android and I don’t make a fuss about it”.

My usual experience with non-computer people is that they really couldn’t care less and glaze over at any discussion of software choices what so ever. I’ve given up even trying to tell them for the most part. If you’re not required to use specific software by your employer (thankfully I’m not), then just use what you want and nobody will care, at least in my experience.

Sadly I can’t. The only approved software I can use is Office on Windows.

I use Libre Office. It runs faster than word.

I only use LibreOffice and don’t tell anyone. It has only been a problem once when a client wanted me to use Word so she could keep track of changes. As a freelancer I wasn’t about to go and use Word for one client. I just submitted the work as a PDF and they never brought it up again.