Got it to work! Thanks for the tip, Ibuyss! Setup is Apple Time Capsule (old flat version) and AppleTV 4K 32 Gb.
The thing is that you need to change the name of the Time Capsule to the port number (I changed mine to 1024) and NO LETTERS in the field. So go to AirPort Utility in a Mac or iOS and change the Time Capsule or AirPort name to just a port number (not sure if other numbers work. Used 1024 as that port number worked on my iOS VLC apps) then restart/update the Time Capsule/AirPort. I initially tried a name with colon then port number, but it didn't work since VLC TVOs turns all punctuation into dashes. I guess the server name field in TVOS is now actually the port field?
At least it's working again until they make another update.
Thank you, this worked for me.