Github doesn't need to know how you implement it, just that your browser is handling it (and in this case the browser lets Bitwarden handle it lol)

I don't think that github has to know that. You could be using a password manager and choose to make it a minimum character boring password or meet minimum complexity requirements or use the same password on a million sites. You have to secure your credentials; complying with the minimums of a service isn't security.

A securely stored modern certificate is going to be magnitudes more secure than password plus MFA.

The certificate path uses cryptography to prevent disclosure of your secret, and can't be compromised when the site inevitably gets hacked.

I wouldn't classify passkeys as MFA tho, they are a passwordless method that's more secure than most MFA methods. Afaik it's based on signed certificates or something like that and that's virtually unhackable unless someone gets physical access to your device (and that's game over anyway).

If you're using software that properly uses your device's SE / TPM chip then it's much more secure against malware, etc. And the main selling point is the much stronger phishing resistance (can't trick you into logging in via a fake site, etc)