Hmm, seems like a softbrick. XDA forums will be able to help. In short most Xiaomi phones have two contacts on the inside and if you short them, they will hard reset the phone and then you can upload your bootloader and or operating system.

Charge it to full and hold power and volume up or down. One of those combinations should give you a menu to wipe phone's memory and get a fresh start. If it works, it should solve your problem easily. If not, try connecting to a computer and listen for the "device connected" sound of your preferred OS. That'll tell you the phone is connected. Power+volume down should reboot your device if it's stuck. Maybe it'll connect then if it can't when you first connect it. Then see if Xiaomi's software detectes it and install the firmware again. Remember to let go of the power button right after the poco logo shows up. Or a Xiaomi logo. Each time you try it. Hope something works and you get your device back. Updating/reinstalling firmware instructions should be readily available with a quick google search also. Take care.