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.
To pile on this, you can point people to public Auth apps that aren’t linked to your workplace. This might reduce suspicions about you installing work apps on their phones.