Could’t find any custom roms but you could try this (originally made for a12 but should work for all A series phones)
It is very possible, samsung only locks down phones in northern america (where they’re forced by the carriers)
You can use the leaked official tool (odin) or the foss reverse-engineered heimdall
The best would be to hack the bootloader and install degoogled android
iOS is a black box so we don’t know what spyware there is
Because everyone already knows about tails