No yeah this was something I picked up during my group project in final year of my engineering degree, but also a quick google shows it holds true still. The first page of results has a lot of random sites that say the same thing. You should typically only discharge to 20% where possible, also it doesn't matter if you charge to 100%, 90% is fine, you should be aiming for as few cycles as possible so if your phone does 1.5 or 2 days between 90/100 and 20 then you should try and let it do that if you can. Over time the degeneration due to normal use will eventually be such that the discharge rate will likely increase to land on charging every night.

This is pretty outdated. The best care for a battery is try to keep it at 50%. The absolute best way to use a battery would be keep it between 49-51%, which is obviously impossible, so people say keep between 20-80, the closer you get to extremes, the more damage it does to the battery (with fully dead being by far the worse)

Depends on the battery, different tech has different best practices.