When I log in through the browser, 1Password asks for my Yubikey first. Only if I cancel that, does 1password allow me to pick TOTP to log in.
However, on the Android app, when I tried logging into my account, I was neither asked for the Yubikey, nor was I given the option to use the Yubikey. I had to use a TOTP to log into the Android app.
I use my Yubikey to log into GitHub on Chrome for Android, so I'm pretty sure my Pixel 3 supports Yubikey.
1Password Version: Android 7.3.4
Extension Version: Firefox 1.17.0
OS Version: Android 10
Sync Type: Not Provided