A friend of mine is not happy with E/OS on her Gigaset GS290 Phone. Bad signal with 4G, wifi and even calls. How can she do a reset to stock Android? If she resets it now it goes back to e/OS.
Works as designed.
An Android so-called “factory reset” in general leaves the installed OS as it is (that’s why it also doesn’t help with issues caused on the side of the OS), it just wipes the data and cache partitions, thus mainly deleting user data as well as Apps installed by the user and their data. The unchanged OS will afterwards present its own initial user setup again.