Forget co-opted as a caveat - it is irrelevant. Co-opted and elected members differ only in the means by which they are returned. In all other regards, there is no difference between them.
Unless you are suggesting irregular practice in the process of co-option?
Also, I don’t want to say ‘forget protest’ because that’s not what I mean, but it must be properly focussed otherwise your momentum will be knocked and you might lose energy / support.
You cannot remove a Cllr with protest unless their moral compass leads them to resign.
Focus on what CAN be achieved within existing legislation.
Ignore unlawful ban from public meeting, video record everything and publish on YouTube, engage local community, ask questions and insist on answers, use the ICO and the external auditor (for what they are worth) publish, publish, publish!
It DOES WORK! I’ve done it!