Is there a way to make a rotated L (or reflected Gamma), like \forall and \exists?

[half junco]

I mean like this.

Can you get it without additional packages? I need it for obsidian notes and I don't know how to add them there.

[serene jetty]

obsidian does not use real latex but a lightweight emulation so this is impossible

you might be able to get pretty close with a Unicode substitute though, eg

⅂

[half junco]

That'll do, thank you

[half junco]

Can you tell me more about which exactly parts of latex are possible with obsidian?

[serene jetty]

Basically only math mode commands are implemented

[lavish raven]

obsidian uses mathjax, so you can look up what that supports

[torn stone]

detexify can't quite find it, but \rceil is your best option. otherwise, you could try to crazy LaTeX shenanigans to reflect a \Gamma, but I doubt that's possible in Obsidian (MathJax).