The problem is you need the exact customt TWRP recovery AND exact install .zip for the model number. There is no unversal twrp file or universal android, or utbuntu. Each manufacturer, model, useds a 'custom twrp file. and unique identifier for android 'custom' rom even for android itself.
if you install wrong file not for the particular device, it won't work and you need to customized or find the exact model rom known as custom rom. even if the phone is running android. you can only flash the manfucturere rom for that device. or c ustomized it yourself
oem unlocking just means you can FLASH it. most devices now have oem locked and you cannot flash anything on it. improperly flashing wrong rom can brick the device and if there is no custom rom for download, there is nothing you can do. you have make one for yourself which needs the manufacturers drivers etc.