Tildes is the only other reddit alternative I've been using. It has really high quality content, but posting there can be intimidating if you don't have 20 minutes to write something insanely detailed.
I haven't heard that - I suppose it's possible, but if I had to guess I'd say they probably wouldn't be interested. It's even more niche than Lemmy in my opinion
kbin.social is only PWA right now. There is Interstellar app for Android being developed right now, but it is available only via Github releases (no Google Play nor F-Droid). And it works only on https://kbin.earth (or instances of /kbin fork called /mbin) right now.