The Poco X3 Pro is notorious for motherboard failures caused by thermal expansion fracturing the solder balls beneath the Snapdragon CPU and UFS chip. If software flashing fails to resolve the issue, the phone will require a hardware repair known as a at a professional service center. If you need help finding specific community links, tell me:
Before using any Firehose file, compare its MD5/SHA1 with known good hashes posted in the XDA thread. A corrupted or malicious loader can short-circuit your device (rare but possible). patched firehose file for poco x3 pro link
Trusted Android service websites (such as HalabTech or GSM Forum) archive functional programmers for specific device chipsets (Snapdragon 860). The Poco X3 Pro is notorious for motherboard