I’m remembering this specifically from a UK point of view, but definitely was the case for US TV also.
In the 90s I used to watch The X Files, Strange But True?, Fortean TV, Eerie Indiana… GhostWatch was a one-off that unfortunately I missed at the time.
There might be a couple of other shows I’m forgetting…
But looking back it seems cool to me that mainstream TV was so into “weird” stuff back then.
Unsolved Mysteries was another good one! Not sure if they aired that in the UK or not
Intro Theme
Beyond Belief: Fact or Fiction was another great one, in this similar vein.