Your phone should have a locked bootloader, as it ensures the integrity of the software running on the device. This is especially relevant for Xiaomi phones, which are often loaded with all sorts of crapware by shady merchants. These vendor ROM's are a serious security risk. You really don't want to run that shit, so do your research very carefully when importing a Xiaomi device to ensure it hasn't been tampered with.
So, Xiaomi makes these nice phones and those vendors just ruin it all. They do the logical thing and start locking devices. But even today, vendor ROM's are still a thing! Even the brand new edgeless Mi Mix isn't safe.
How is this possible?
Through a wide open back door called EDL mode. To flash anything you want, all you need is a "deep flash cable" from [Aliexpress](https://www.aliexpress.com/wholesale?catId=0&SearchText=xiaomi+deep+fl