Vinegar is a Safari extension for iOS that turns the YouTube media player into a generic iOS one, completely bypassing all of these restrictions. I’m not savvy enough to know if it’s something Google can kill or not, but it’s working great for me right now. Even lets you do PiP and background play.
Guardians 3 has a lot of heart and stands shoulder-to-shoulder with some of Marvel’s best. Just watch it as the end of a trilogy of Guardians movies and don’t worry about the greater plot of the MCU.