You need to return that phone ASAP and get something that will let you install a custom ROM on it, like a Pixel or a OnePlus.
Edit: shitsung just recently sent out an update that finally kills off bootloader unlocking for all shitsung devices. Us Americans haven't been able to do it for quite a long time, but Europe and Asia could, and now they no longer can. So shitsung is absolutely not a brand to be using at all.