I mean, this one is on me. I bought Poco X3 Pro knowing damn well it's plagued with issues. But €188 for phone with Snapdragon 860, 120Hz screen, big battery, stereo speakers, headphone jack and IR blaster 1 and a half years ago? Hell, that sounds too good.
And yes, before you ask, I have tried turning it off an on. Also resetting both from settings and recovery.
If it was a motherboard replacement, it's entirely possible they missed connecting the cable for the camera entirely or just didn't get it fully connected and is loose.
It's possible (the partially connected bit) since I previously got an image from it. Kinda. The camera app still didn't work, but CIT test menu gave me image with only small hint of color.
Edit: On the other hand, all 5 cameras don't work, which is suspicious. Maybe some calibration?