If you want people to give up flying you need to give them alternatives. I always choose train if it's available. And for meat we don't have to collectively give up meat, eating less meat (once or twice a week) would be totally efficient in limiting the CO2 emissions
I see nothing wrong with apps for lemmy grow. Every new ex-reddit app that makes a version for lemmy means more people will stop using the reddit app and use lemmy instead.
Libraries are one of those concepts that sound very alien to today's mentality "what do you mean free renting of copyrighted material without paying the owner company?!"
Thunder and sync are the ones I use the most but they're almost all good, if one has a bug I just switch lol