For our business we use a number of different apps and websites but only two of them offer 2FA with a security key. The rest allow for an authenticator app. In this case, it seems just using an authenticator app would be best for consistency and without needing to purchase keys.
Of course, installing authenticatior apps on each device would be a no-no since it wouldn’t technically be 2FA. Then do we use each employee’s personal phones? Not sure how to proceed.
I would just give them a Yubikey or something similar and then they don’t need to use a phone to store the TOTP codes (the app for that purely accesses the data on the key, there are desktop applications for that too) and for webauthn you want to connect it directly to the work device anyway.