Protests IRL are disruptions to spaces and functions such that normal people learn about and become sympathetic to your cause.

So it would need to include:

• Disrupting people’s normal flow
• Messaging them at that moment of disruption

wikileaks

It would probably be almost indistinguishable from cyber warfare, which would be both a positive and negative.

Something like an injected pop-up telling visitors to a company or utility about their shady business practices, etc.

Obviously, the downside to this the risk of public opinion turning against your protest. Upside is that the tools needed are already highly developed by the illicit market.