What Is The Highest AC Possible In D&D?

How THICC can we go in Dungeons & Dragons? Spoiler alert: nothing can hit you without a crit, and you still have about 40 AC to spare on top of that. This build assumes no “outside help“ i.e. no Dungon Master created special boosts, or Wish or homebrew items. See the pinned comment for more info on improving it!