Have you ever REALLY scared your players?

Howdy!

I have been GMing for almost a decade now for various games and I have a attraction to horror as a genre. I have run a few Monster of the Week games and lots of horror themed D&D and in all of my time I have only really truly scared my players a few times!

I get feedback that it is always engaging or intense and I can tell my players enjoy the horror vibes but I really want to scare them you know, make it hard for them to sleep once they get home.

I ran my first session of Mothership a few weeks back (if you haven't tried it yet I recommend it highly!) and I have another session coming up here soon. The session was a ton of fun and everyone really had a blast but the main feedback I received after was that my monster wasn't scary. I feel like TTRPGs are a challenging format to really create true fear, after-all in reality you are sitting around a table with your friends rolling dice. So here is my question:

Do you have any tips on what you do to really elicit fear in the TTRPG format? Or maybe you have scared your players before and have some thoughts on how you managed to do it.