Disclaimer - This is not a promotion of a channel, i just thought it is really a cool thing and would help people.
Recently a youtube channel New Rockstars, that covers shows and movies and explains ending and theories, Came up with a plan i.e Road To Doomsday where they are going to be discussion and explaining everything in MCU, so for people who didn't have an opportunity or time to watch the entire MCU and feel left behind can watch all or some of it they feel they are lagging behind, maybe it will be helpful and would let more people enjoy Endgame.
PS - They won't allow me to add a link to video but you can easily find it.
Catchup for Avengers Doomsday