Idk if latex is optimal for note taking, or if others will warm to it if forced, but overleaf is obv collaborative though not selfhosted.

I’ve liked Outline https://www.getoutline.com/ and while I haven’t used it collaboratively, it really highlights that it’s a primary goal. It’s supposed to be a collaborative/dynamic wyswyg wiki thing. You need a SSO service like authentik or authelia for it, it doesn’t do login. But that’s good for security anyway!