I’m having the same issue. It’s related to LibraOffice because the upload (a resume to LinkedIn in this case) doesn’t work. I was using a previous version of LO, where the save type for .docx stated 2007-2013. I also tried to save it as a .doc, and updated LO (126.96.36.199 (x64)) and noticed the .docx format supported 2007-2019, so I thought that might help, but I’m still having problems. Export as PDF works fine. I don’t have MSOffice at home like the OP so I can’t test that, but there is clearly an issue between how LO saves as an MS file to where LinkedIn continually says only Microsoft Word or PDF. I also tried to save it as a XML doc (.docx) and that doesn’t work either. If the file format says it’s a .doc or .docx … third party apps need to “think” it is truly being saved as an MSOffice application document. Otherwise, it’s not really masking the save as that format.
I tried the save as as the first answer suggests and it doesn’t work.
I also tried the second answer, this doesn’t w