I have the same issue, the rotate works fine for playing in VLC (For some of the transform options) however when playing in windows media player it's back to vertical, and or uploading to online video players. I used these instructions
https://www.maketecheasier.com/rotate-vlc-video, as well as instructions that had me go to advanced preferences > Stream Output > Stout Stream > Transcode > Video transformation
https://www.howtogeek.com/14751/rotate- ... n-windows/.
I tried with a few combinations of Stout Stream and Video filters Stout on Video filter off, none of these options that I tried have been able to get it to play in a different player with the rotation and only some of these get it to play in VLC with the rotation after it's saved.
With these same videos I have used VideoProc Converter AI as well as ClipChamp and the same thing happens, for the app that converted it, the video will play with the rotation but if I use a different app other than the converting app it goes back to vertical instead of the horizontal rotation that it was exported/saved as.
Edit: Correction Clipchamp actually does appear to work with it's exported rotation to play in VLC.
I have seen that there could be some metadata that tells it to play vertical and that this could be stripped I'm looking into this now if someone knows how to do this already I would be happy to hear : ).