who owns the content generated by the users? what if i as a user give twitter sole rights to my content

> the only legal hurdle would be complying with takedown requests.

If you mean 'takedown requests' related to X content that should not be a problem since nitter does not cache content so anything taken down by X is inaccessible to nitter. If you mean takedown requests for nitter instances the question is on what grounds those requests are made - TOS violations or legal grounds? If it is the former it would be easy for X to just block the user IDs and no takedown request is needed. If it is the latter, which laws would those be based on?