My desktop doesn't have Bluetooth. Does this mean I'd be doomed even if I had a compatible mobile device?
We might need to redo this whole Internet thing because this is insanity.
Yes. The technical name for this FIDO2 QR code flow is caBLE (Cloud Assisted Bluetooth Low Energy).
In a free market, the content provider is free to put whatever guardrails they feel appropriate. Loginwall, Paywall, CaptchaWall.
If you don't like that provider, you are free to pick another.
I also disable Bluetooth on my phone every few months (and never enable it)... or at least after every CCC or such.