I was just struck out of nowhere at 3am with a memory of watching this in prep for Loki S1's premiere. I think I finished it day-of (west coast getting Disney+ "midnight" drops at 11:50pm the date prior, because we're better than everyone else), so hopefully this date is right. If it's not, it can't be far off.

But I just checked my list of 2021 movies that I tracked before Letterboxd, and one of the ones without a date was indeed Avengers! So I'm feeling pretty certain about this having happened and my having nailed the date.