You really shouldn’t use SMS 2FA. SIM swapping does happen. This kind of depends on the jurisdiction though. In some countries operators won’t reassign the phone number willy-nilly.
Still, better to just not do SMS auth. These days Yubikeys are not that expensive. Get three, register them all at the most important places, and put one at a parents’ place or similar.
But the point I was making that IF the website does not allow Yubi THEN SMS is almost certainly available, and you should use that as a backup mechanism.
Why ? Some sort of backup mechanism is better than none at all.
Still, better to just not do SMS auth. These days Yubikeys are not that expensive. Get three, register them all at the most important places, and put one at a parents’ place or similar.