There are real, impactful things you can do as a leftist that would be very unlikely to lead to reprimand or violence. You can:

• provide childcare/other care/cleaning for someone who needs a break
• volunteer with existing community orgs that do good local work even if they are not "leftist" enough for you. You'd be surprised who you meet, and who else is not shouting their beliefs from the rooftops.
• teach a skill
• organize to buy things in bulk and splitting them to provide cheaper prices to all participants (lower food costs for example)
• organize a group of people with diverse skills so that they can help each other, without exchanging money.

Honestly, volunteering with existing "above ground" orgs is really my top suggestion. It teaches you invaluable lessons about organizing, sustainability, and cooperation. It makes real impact to local communities and helps you meet your neighbors.

I think there are a lot of expectations that flashy protests or action is where change happens and that it's a sustainable approach for an individual. They are important, for sure, but they don't get the washing done! And they wear you down. I'm speaking from 20+ years experience.

The other thing I want to say is that in many cases the people who are doing the things you are afraid of are not afraid, and that's why they are doing it. That doesn't make you less. Maybe they hate a task that you are really good at and enjoy doing. It takes a team to make things happen, and everyone is an important part of it.