Two-factor authentication not working with Wi-Fi calling after macOS Tahoe upgrade

MANY OF MY ONLINE RELATIONS LIKE BANKS, COX CABLE, ATT, SCE, SOCALGAS, ETC. US 2FA (TWO FACTOR AUTHENTICATION - THEY OPEN A FIELD ONSCREEN AFTER I LOGIN AND SEND ME A CODE ON SMS - GENERALLY A 6 DIGIT CODE ON A SHORT MESSAGE FORMAT - NOT A FULL PHONE NUMBER BUT GENERALLY A SHORT MESSAGE OF 6-7 NUMBERS.

NOW THAT FEATURE WHICH ALWAYS WORKED BEAUTIFULLY FOR YEARS DOESN'T SHOW UP ON MY PHONE. IT'S SOMEHOW BLOCKED WITH WIFI-CALLING AND SHOWS UP LATER WHEN I GET ON A CELL NETWORK. MY HOME IS OUT OF CELL RANGE SO WE ONLY USE WIFI CALLING WITH AT&T AND IT HAS WORKED FINE FOR YEARS. NOTHING ARRIVES.

NOW I HAVE WORKED THROUGH LISTS OF HOW TO FIX IT FROM MANY SOURCES BUT SO FAR NONE HAVE WORKED. SOME ARE OBVIOUS LIKE MAKE SURE YOU'RE ON THE SAME WIFI NETWORK AND RESET THE PHONE, AND SOME ARE NOT SO OBVIOUS LIKE RESTART YOUR LAPTOP.

SEEMS HARD TO BELIEVE THAT NOBODY ELSE HAS THIS ONE?

ANYONE KNOW OF ANY ONLINE TEST SITES THAT CAN HELP ME QUICKLY AND SIMPLY TEST BY 2FA?

[Re-Titled by Moderator]

Original Title: TWO FACTOR AUTHEN DOESN'T WORK WITH WIFI CALLING AFTER TAHOE UPGRADE