I've found that OnlyOffice has much better Microsoft Office compatibility. I just install it via flatpak, remove the network permission, and go about my business perfectly. While LibreOffice -> LibreOffice works perfectly fine, whenever it opens a .docx file it always wants to save it as a .odf which is a nonstarter. Not because I don't want to support open document formats but because everyone expects a .docx back if they send you one. It also struggles consistently for any type of advanced formatting (as a .docx).

Remove the network permission by what mechanism? I only know firejail or this (iirc)