That's not true though. Posting/commenting radical thought is a role that helps. Sure, it's not much, but it's certainly not nothing.
When there's an open investigation against me and I have to lay low for a while, it directly improves my life to have leftist content to enjoy, which in turn keeps me going so I can continue to improve the lives of others
Someone spending their time making a meme for a leftist community is also effectively making propaganda that I'll later text to someone, which may further radicalize them, even if just by a little.
Marx himself literally said:
All social life is essentially practical. All the mysteries which lead theory towards mysticism find their rational solution in human praxis and in the comprehension of this praxis. (8th thesis)
Just because social media didn't exist then doesn't mean it doesn't count now
Edit: also, within this specific context, it definitely can directly improve people's lives to see allyship simply signified both in-person and online. It personally makes me feel safer, and that's important