It’s not my preferred method because I want 2FA to save me if my device is compromised, but it does still add protection against traditional password attacks, credential stuffing, etc. It even adds a layer of phishing resistance, as long as the user doesn’t blindly jump to copy/paste when autofill fails.

What is the phishing resistance it adds? Bitwarden auto copies TOTP to the clipboard.

Depends on the password manager. 1Password will not autofill if the domain doesn’t match. It’s up to the user at that point to check the url before copy/pasting the code. My guess is that the average user would do that by reflex without a second thought.

2fa is mitigation for weak passwords. With a password manager you can use a strong password, and 2fa becomes redundant.