Hi Gabriel and thanks for your reply.
I've already taken practically all extreme measure...
Referring to our questions - The TV's firmware is up to date, I had reinstalled the app (there is no option to remove it as it is preloaded by Samsung), I had reset the TV to factory settings, I had reset the app (inside the app), the internet connection is super and all other TV streaming services work great (as did the Apple TV app until a day before).
This issue does not occur on any other device. However, out of several devices running AppleTV, this is the only TV running the AppleTV+ app version 1.0.2.
The rest (newer Samsung TVs) run the AppleTV app (no +) version 13.4.0.
So my guess is that Apple changed something on the server side that led to this malfunction of the AppleTV+ app.
Please help...