Not receiving 2FA verification emails

I am completely locked out of my personal Microsoft account because i do not receive two-factor authentication (2FA) verification emails.

The strange part is that password-reset emails arrive immediately and without any problems. It is specifically the sign-in verification codes that never arrive.

What happens when I try to log in:

1. I enter my Microsoft account email address.

I enter my password.

Microsoft accepts my password.

Microsoft asks me to verify my identity using my registered secondary email address.

I select that email address.

Microsoft claims to send a verification code, but absolutely nothing arrives.

What I have already tried:

Checked my spam/junk folders.

Checked other inbox folders.

Added email filters to explicitly allow Microsoft's emails.

Changed my registered secondary email from iCloud to Gmail (a completely different email provider/domain).

Successfully verified the new Gmail address.

Waited the full 30-day security information replacement period.

Confirmed that password-reset emails arrive immediately at the registered secondary email.

Used Microsoft's account recovery and self-help procedures.

Tried Microsoft's support chatbot using a separate Microsoft account.

None of these things have resolved the issue.

I do have access to my connected additional email account, just to be clear.