Yubi keys no longer available for 2FA? Why?

There is a github blog from August 2021, which promotes using Yubi Keys for 2FA.

Just tried to enable 2FA on my private github account and it is not offered any more.

I checked on my company account, where we activated YubiKeys for a group of developers in summer this year and I can see, that the option “security key” is activated there.

We like to have this option for a new developer and now YubiKeys are no longer offered. Our company policy does not allow the usage of personal equipment (smartphone) so Yubi Key was a good and cheap choice.

Can anybody explain why this option is no longer available and if it will become available again in the near future?

Thank you