2 hints:
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Ubuntu - OnlyKey App - Please connect your OnlyKey - #9 by Mango_Mungo
~# apt install libu2f-udev -
Yubikey OTP with Yubi cloud sucks. Maybe Time-based One-time Passwords (TOTP) is an alternative. I use the TOTP from andOTP or FreeOTP+ with OnlyKey.
Both apps at Free and Open Source (FOSS) software archive for Android