If you're in this category, your alternative to Passkeys at all is SMS or no 2FA whatsoever. Enabling Passkeys does at least ensure that you have a minimum of two separate devices so you already do effectively have some form of backup of your second factor.

My comment is targeted at someone who is savvy enough to: a) care about having "real" 2FA, and b) is concerned about lock-in, and c) is extremely sensitive to being locked out. For someone like that, you're already buying YubiKeys or some equivalent. And if you don't already have some, you're never prevented from using them later.

Reminds of the occasional comment threads on here about homeless people permanently locked out of new accounts every few months because of stolen devices and the growing corporate obsession with forced 2FA, and all the replies that amount to "if they didn't want to fuck off and die they shouldn't have been poor".