That will depend on the site. It's not a new problem to think about either. For instance, you can set up multiple MFA mechanisms on Google, and I believe you c

That will depend on the site. It's not a new problem to think about either. For instance, you can set up multiple MFA mechanisms on Google, and I believe you can set up multiple U2F devices for any given account. To this day you cannot set multiple MFA devices on an AWS account. No, enrolling multiple devices at the same time from the same screen does not count.