Aside from platform agnostic password managers having support for it as a commenter below pointed out you can also save it on a physical “hardware security key” (e.g. yubikey). Technically this should be the best option as there is no way for anyone to steal your passkeys unless they physically take apart your hardware key (and there’s even keys that have additional protections that make it impossible to take apart without destroying it).

However every single platform really pushes people towards using their own solution. So only their solution is neatly integrated in their platform and also preselected when you save a passkey. But all in all those are rather small hurdles for the security a hardware key gives.