Yes, they exist, but there is no reason to use them other than tinkering around. Also they have much worse security than Android or iOS. So if you need something private and open source there are a plenty of degoogled Android ROMs.
Graphene OS - best privacy and security, only for Google Pixel phones
Calyx OS - less secure but supports cheaper phones (Motorola) and eco-friendly phones (Fairphone)
Honorable mentions are LineageOS, /e/ OS, Replicant and iode OS, however their security is much worse than of Calyx/Graphene (no verified boot), so use at your own risk
Yes, they exist, but there is no reason to use them other than tinkering around. Also they have much worse security than Android or iOS. So if you need something private and open source there are a plenty of degoogled Android ROMs.
Suggest one of them too
Graphene OS - best privacy and security, only for Google Pixel phones
Calyx OS - less secure but supports cheaper phones (Motorola) and eco-friendly phones (Fairphone)
Honorable mentions are LineageOS, /e/ OS, Replicant and iode OS, however their security is much worse than of Calyx/Graphene (no verified boot), so use at your own risk