Going to Mi centre is of no use.
Hope you have backed up your data.
Only solution is resoldering CPU/RAM.
Some people do it.
Rest, nothing else can be done.
Wait for BBD, buy a new phone, anything except Poco.
Do tag them in Twitter, so other people searching internet also find this.
Mine Poco X3 also was dead, resoldering didn't work for me though. So bought a new phone.
I can’t forget this phone, bought as developer phone and once I got the news of dead MB in telegram groups, I sold it on cashify for a cheap price. It was 5-6 months old unit. I was a developer and helped in a lot of roms for this phone (cheap phone/good config).
Even though Poco offered 2 years warranty, horrible experience in the service centre and now I don’t recommend anyone to buy Poco phone.