Think back to the times of slavery. You could've said: "I don't own any slaves, so there's nothing I can do". In the end, we did the right thing, but unfortunately after much human suffering. Hopefully we don't wait even longer this time around. There were many things you could've done to help. You could've avoided buying from places that used slave labor. You could've voted for abolitionists. You could've donated to the cause. You could've stood for justice when serving on a jury. You could've convinced your friends that things had to change.
You as an individual may be individually directly responsible for a small amount, but you are probably responsible for a greater than average amount. The little changes that you make will make a bigger difference than most people's. You can also be indirectly responsible for a much greater amount. Talking to your friends about the environment can have a greater effect than you acting alone. People don't realize just how much better EVs are, induction stoves are, heat pumps are, solar panels are, etc, if they haven't heard the benefits. Help to open their eyes.
Your vote also likely controls a far greater amount than you are giving it credit for. Margins of victory are often small, and a few people thinking of the medium and long term can make a big difference.