I fixed it with those solutions too at first but there were these ugly programs in my applications so I fixed it with WinUtil Documentation instead as well as the tool can do a great other many things to boost performance and privacy. I used the config tab to install legacy media features
So, downloading the AC3 Codec worked for me, but now when opening the plex app it will either cut all other audio playing if I open it with other things playing (ex, Youtube via Firefox) or if it is the first app I open, all other apps will then not have audio working as well.
Exactly what needed to be done. A little disappointing that plex could not resolve the issue themselves. Thank you to the person who posted the link to the fix, and truly thanks to the peeps that created the fix.
This did it for me. Built a new PC and ran into the same issue, installed the “DolbyLaboratories.DolbyDigitalPlusDecoderOEM_1.1.285.0_neutral_~_rz1tebttyb220 (1).AppxBundle” Windows app from the MajorGeeks download you linked. After installing I closed/re-open the Plex Desktop app and I have audio again on the videos that previously had no audio!
This is a Windows 11 issue and not exactly a Plex issue, but I can understand people’s frustrations.