I just wanted to chime in to say this fix worked for me. I was frustrated that after this latest update, Designer kept opening in the old version. I would try to run the update again, and it would say "This is already installed. Do you want to launch it?" And I'd say Yes, and then it would open the correct version. But I couldn't for the life of me figure out how to set it to remember to always use that version, or how to get rid of the old one.
Anyway, yep, turns out I had previously install the .exe for the last version, and this time I used the .msix. I got the new .exe and installed that, and everything's working as expected now.
Thanks for the info Walt!