Like many things, it depends. I'm curious about the context where you're actually hearing YouTubers say the letter.

It's usually "zed" and we're taught it as "zed" in school - at least when i was a kid.

If I'm spelling something it is Zed. I don't think I've ever said Zee in that context.

The alphabet ends with Zee when singing it, due to the rhyme with Vee (and probably Sesame Street).

In my head I will say Nissan Zee for a Z type car. Though if I was to speak the phrase "Nissan Z type" I would say Zed.

When it is used in online slang (GG EZ) it is "Zee" for "easy".

ZZ Top is Zee Zee Top. Zorro draws a Zed. Things are Zed-shaped, not Zee-shaped in general.