I'm also quite ignorant of investing and also contract law, but technically, Robinhood's recent disabling of buying new options or shares [1] falls under their terms of service [2]:

You agree that, without notice, _Robinhood may terminate these Terms and Conditions, or suspend your access to the Service or the Content, with or without cause at any time and effective immediately._ [...] Robinhood shall not be liable to you or any third party for the termination or suspension of the Service or the Content, or any claims related to such termination or suspension.

tl;dr: we can change what you can do on Robinhood at any time for any (or no) reason at all, and you can't do anything about it.

[1] https://old.reddit.com/r/wallstreetbets/comments/l6w4uo/robi...

[2] https://d2ue93q3u507c2.cloudfront.net/assets/robinhood/legal...