#Dual-wielding Monk
Dual-wielding Monk
A simple way is to be a Monk with the Dual Wielder feat, 20 Dex, and 20 Wis. This gives you a 20 AC from Unarmored Defense, with +1 from the Dual Wielder feat for a total of 21.
This can be increased by 2 in most combat rounds if you're a Kensei. If you use a kensei weapon and a monk weapon in your hands to count as dual-wielding, you can make unarmed attacks by kicking your enemies. Any round you kick using your Attack action gives you +2 to AC from the Kensei's Agile Parry feature, for a total of 23.
#Defensive Style
Defensive Style
A Fighter, Ranger, or Paladin can take the Defensive Style feature, which gives them +1 AC when wearing armour. This gives them a maximum of 21 (18 from plate, +2 shield, +1 style).