Why am I not receiving 2FA texts after iOS 18.5 update?

You will need to contact the financial institution to determine what they have on file for your 2FA contact. If it is a text message, there may be a problem with what they are sending. Do you have RCS Messaging turned on? They may be using that if they are sending an SMS/Text message and if you do not have it turned on, you wouldn't get it. But they are responsible for what is sent to you, so they will need to troubleshoot it.

You're welcome. I have a few 2FA accounts that are delivered via email, and while you expect them immediately, especially since many of them are only valid for 5-15 minutes, some are just at the edge of the expiration time. While I like the concept of 2FA, sometimes it doesn't really work as good as it should.