PlayStation 4 picture only there briefly and then away again?

My family has had a PlayStation 4 Slim for a long time, but I don't think they have ever used it.

Now wanted to use it to watch blurays and DVDs.

Unfortunately, the TV (OLED) recognized that something was connected via HDMI and even indicated that it was a PlayStation, but always only displayed "No signal" on the screen. Of course I tried all HDMI inputs, but without success.

Then my thought was that maybe it is because the PlayStation is not yet set and the "modern TV" may therefore have problems. So I got the old TV (small Samsung flat screen) from the basement and tried it. At first nothing came, but at some point I had it so far that it shows a picture at irregular intervals for 0.5-3 seconds.

I then used this to regulate the resolution to a minimum in security mode.

Was also a bit problematic because I had to reconnect the controller (or rather "the" controller - tried several) to the PlayStation again and again. In the end it didn't change the problem.

My brother later brings me another HDMI cable, which I then try again. Is there anything else that could be the reason? (except for the obvious that the HDMI output on the PlayStation is broken)

Thank you in advance for everyone who tries to help me

Someone "tapped" it and applied some finger fat to the contacts. Get a clean handkerchief from a pack that nobody has attacked yet. Carefully polish the HDMI connector (do not press!).

At most, you can also use very little alcohol.