Guide: [ Ссылка ]
In this video, we will show you the steps to install the firmware/ROM on your Android device via the ADB Sideload method.
The biggest advantage of this method is that it doesn't require an unlocked bootloader. So you could easily use ADB Sideload on a locked bootloader without the need for a factory reset or voiding your device's warranty.
On the other hand, if something goes wrong during sideload, then it could prove to be a difficult task [as the bootloader is locked so you cannot use the flashing process]. Apart from that, you cannot use this method to perform a downgrade.
You can only use ADB Sideload to install the same or higher version of the OS, never the older version!
If we talk about sideloading custom ROMs, then they usually do require factory reset [either before or after flashing the ROM, verify with the respective developers], however, in those cases, you cannot use the stock recovery for this task. ADB Sideload with Custom ROMs is only possible via a custom recovery [such as LineageOS Recovery or TWRP].
