Tried the twitter pwa again, and immediately uninstalled *again*.
Somehow twitter are completely overriding #a11y settings on font size. My font scale: 200%, my blog for reference, then pwa. Still tiny font. No idea how they're doing it, but it's unusable for me.
I've *just* found a setting tucked away which lets me control twitter's independent font scaling. It's a touch bigger, still smaller than the native app font size.