Well, because I like playing devil's advocate, I will try to break the game.
Bounded accuracy depends on AC not getting too high (Ac 28 seems fairly unhittable by anything other than a crit). Because attack bonuses are fairly fixed.
+1 Full Plate, with a base AC of 19 (19)
+1 Shield will add +3 (22)
The level 2 Druid/Ranger spell Barkskin will add +2 (24)
The 3rd level Wizard spell Haste will add +2 (26)
The 1st Level Cleric spell Shield of Faith will add +1 (27)
The 3rd Level Cleric spell Prayer will add +1 (28)
A Ring of Protection will add +1 if Attuned (29)
A Dusty Rose Prism Ioun Stone give +1 (30)
A Pale Green Prism Ioun Stone give +1 (31)
Mountain Dwarf +1 (32)
Fighter Defense ability +1 (33) (You could go with protection for forced disadvantage, which is better than a +1 AC on average, but it's only once per round).
So you can get up to an AC 33, with just +1 items. It's unclear to me if items will go to +2 or more, so obviously it could go higher.
I am not sure anything in the game can hit you at AC 33, baring a crit. A Balor, for example, has a +8 attack.
Now +6 of that is from spells, but +2 of it is from a Ranger spell, and Rangers get the Defense ability as well, so this character can be a Mountain Dwarf Ranger.
It wouldn't be hard to multi-class to get a couple of those, but even if you remove all the spell bonuses you don't cast yourself you're still looking at AC 29. And if you eliminate the Ioun Stone's, it's still 27. That's just your race bonus, your class bonus, the barkskin spell you cast on yourself (lasts up to an hour, 2nd level spell), +1 plate, +1 shield, and a ring of protection. I don't think that's too unusual by mid to high level. And yet, a friggen Balor demon would need to roll a 19 or better to hit you.