Been thinking about purchasing a new iPad Pro which has the USB-C connector so I can use my Yubikey 5c in it. Thus far I’ve not installed Bitwarden on a mobile because I use Yubi-based 2fa, but can also use it in fido u2f mode if that matters and either one is an option.
The 2018 iPad Pro with USB-C severely restricted what could be done with that port. The 2021 M1 models change that quite a bit, and you can use many more kinds of USB-C device, including keyboards. I have not tested this myself (have the M1 iPad Pro, but not a USB-C Yubikey.)
Tested it on my M1 iPad Pro with a USB-C Yubikey (5C NFC). Could use it to login into the Bitwarden App.