Hello! (Read it fully)
I had the same problem, but i finally got it. First download the 12.5.7.0 rom from this page (Fastboot rom)
On this page, we will share all the latest Xiaomi Poco X3 GT (codenamed chopin) firmware flash files. To flash the firmware file, you need Xiaomi Mi Flash
www.getdroidtips.com
Then, go to Mi Flash Tool (also download from that page). The version you need is 20210226
Then unzip the rom as many times as it needs, and copy it (the most decompressed folder) to the desktop. Then, launch Mi Flash tool and install the drivers in drivers page. In the right corner you need to select "Clean all". And.... FLASH!
It solved my problem. I had the same as you. If your computer doesn't recognize your device, stay in fastboot 30 minutes and it will turn off automatically (with usb unplugged) or if it says no digest file found, turning off in 5 seconds turn it off.
I hope this can solve your problem.
Edit: Then update the firmware to 12.5.8.0 OTA way. Don't obey people saying stupidities like "Buy a new one". This is a forum, to help people, and if u don't know the solution, DON'T SAY ANYTHING
Bye