You can absolutely submit screenshots of text conversations as evidence in court. I've literally done this myself.
Someone could challenge the veracity of the evidence if they wanted to, at which point you might want to prove that they hadn't been edited by doing something like showing the copies that are actually on your phone. But you can absolutely submit screenshots.
I would argue that people who hold genuinely socialist views who laser focus on disempowering the left are nothing more than useful idiots for authoritarians and can safely be sorted into the same box as actual infiltrators and parasites. The intent of individuals isn't nearly as important as combating the behavior that's being exploited.