Can't play MP4 videos from youtube or other location

Title says it all. I am unable to play mp4 files from Tumbleweed Gnome 3.28x

When I try, it directs me to install missing codecs.

I used zypper install gstreamer*mp4 as the likely codecs

While that installed successfully, I was unable to reboot
Tumbleweed. Now I have a second installation of KDE,
but I will not attempt to do the codec updates.

MP4 files are the way to view with Firefox.

Firefox doesn’t use gstreamer at all, so installing any gstreamer packages won’t help you.
And actually there are no gstreamer*mp4 packages, so I have no idea what you actually installed that seemed to have broken your system… :wink:
(although a “zypper dup” might fix that, if not you should be more specific what the exact problem is, preferably in a new thread with an appropriate title)

What you need to do is the usual thing:

  • add the Packman repo, if you haven’t already
  • do a full switch to the Packman repo, either by clicking on “Switch system packages…” in YaST or running “zypper dup --from packman” (or similar)

Please post the output of “zypper lr -d” for further help.