A syncable FIDO credential refers to the ability that its private key is synced in some way between different devices.
This is just not possible.
The private key of a FIDO credential created on a YubiKey, by design, is stored inside the YubiKey and is suposed to never leave it [*]. So, by definition, it can not be synced anywhere (whether that credential is a resident one or not).
[*] Except with attacks like YSA-2024-03.