The Boost android client for Lemmy is displaying these dark pattern ads pretending to be system notifications. What security/privacy conscious Lemmy clients do you recommend?

This is why ad blockers should always be used. Small devs don't have relationships with advertisers or control over what ad networks will do.

Or you can pay once and be done with them. I think the price of a burger is not a big ask for something you use every day.

I do both.