Isn’t webview-based still essentially chromium-based?

Not sure tbh, but choosing a more niche instance will at least make your local feed different. Communities in more niche instances might also have less political flow into unrelated posts

It really depends on the instance. The big ones definitely have a lot of politics. More topic-focused instances tend to have less of that.

They don’t need Signal to do any of this though, so this doesn’t seem like a very plausible theory.