Sorry about this. It happened to me with a Huawei phone in the past. I wanted to unlock its bootloader but their server was shut down and it was not possible anymore. Since that day, the first thing I do with a phone is unlocking its bootloader even though there isn’t a ROM to install yet.
Well, they already made it very hard. Their account requires a phone number. You have to use their community app to appeal for an unlock request, and it only works at a certain time on a day. If it didn’t work at the first try, you have to wait for 10 days (this part could be different, 7 or 14 don’t exactly remember). Also. it never works at your first try anyway. They limited the unlock count per account, 3 per year, then they dropped it to 1 per year. Last time I heard it was impossible to unlock older devices because they shut down their server. So the very restricted version of unlocking appeal only works for HyperOS versions I think, so if you have MIUI it’s not possible anymore.
As far as I know Xiaomi stopped letting unlock the bootloader even for older devices, so you’re out of luck I’m afraid.
The bot couldn’t even put the link in the correct place lol
Well, you can say that is an experience.
By the way, this won’t help for your current case but I suggest to track this page for your possible future phones. I know I never gonna buy Xiaomi again.