Upon closer review it appears that the only Yubikeys with firmware version 5.5 were the Yubikey Bio, so I bet the total number of those in the wild are rather low.
Casa recently added yubikey support.
https://blog.casa.io/secure-your-bitcoin-with-yubikey/
Casa supports firmware versions >= 5.5. This vulnerability exists for firmware versions < 5.7. Install Yubikey Manager to check your firmware version.
Upon closer review it appears that the only Yubikeys with firmware version 5.5 were the Yubikey Bio, so I bet the total number of those in the wild are rather low.