Wow there's all kinds of stuff out there on this topic, here's an interesting one, way down on this thread: [Link: us.community.samsung.com] : "I spend a few calls with the german Samsung Support Hotline yesterday and I now have a fix that seems to be working for my TV.

There is a transparent plastic part on the bottom side of the TV and about in the middle of it is a small notch (marked in second picture). Carefully pulling on that notch (take off your add on frame first) makes the whole transpartent plastic unit with all the sensors slide out just a little bit (about the thickness of the Samsung Click on Frame). I could then install my white add on frame underneath that tiny notch so it has a clear view now. Apparently the notch is where the motion sensor is viewing through.

The TV now turns on art mode when I enter the room.
"
Then there is this: "I have a 2019 Frame TV and I found that the following setting had to be enabled for this to work correctly: Settings > General > Smart Features > Autorun Last App."