What do I have to look out for when buying a 4k TV?

Moin, I'm just about to make smart about 4K TV and wanted to ask what I should pay attention. This is used for my Ps4 and movies vil. Is still the pc via remote / cable to it. My buddy says I should pay attention to black values but how will they specify?

Have you had any experience with the brand okay?

Why 4k when 8k is out now? And the ps5 is set to 8k