Pretty much anything with “automagic” properties, anything based on proprietary “cloud”, or anything so big I couldn’t possibly audit it (not saying I audit everything I use, I just want the ability). Oh, and also, products claiming to be “security oriented” when they are, in fact, not.
I sometimes make exceptions for “least terrible in class” when I absolutely have to use a given software or be irremediably cut off from a big part of society, like with AOSP and Signal. But those exceptions are few and far between, so there isn’t a lot of popular software I use.
My general guideline is to ignore what I don’t like, downvote what I find harmful. Of course, the first one is emotionally motivated, while the second is rationally so; and therefore doing this requires a conscious choice. So, when I’m too tired, I might fail at doing this. But that’s the intent anyway.