The fact that two versions are showing strongly suggests that the upgrade that didn’t complete fully the first time, possibly because of the c:\temp permissions issue.
I honestly can’t say with certainty what will happen if you try to uninstall the earlier version, but I strongly suspect that it would damage your Plex Server install since it will be pointing to almost all the same file locations and registry keys.
There is a way to manually remove an entry from Programs and Features, but it involves directly modifying the registry. Only proceed if you are comfortable with registry modification, and export anything from the registry that you are going to modify/delete so that you can restore it if it creates a problem. The Microsoft article is here: PROCEED AT YOUR OWN RISK
