Yubikey does TOTP on-board, but you need to connect it to a phone or computer (no display or on-board power). It solves a different problem, where you want to have your TOTP credentials on a tamper resistant hardware security module. It doesn't solve the "don't want to carry around a phone for TOTP" problem.
This doesnt make sense. If you need a 2FA code then you are obviously using some device like a laptop already. Yubikey totally solves the "need a second personal device" problem.
