I am really wondering what was wrong with the device you have tested Apex on. Today i played it on my F4GT (MiUI 13.0.8) for nearly 3 hours without a cooler at 22C room temperature. Maxed out on highest FPS. The temperature of the RAM (the one you see in the monitor from dev options menue) was at a peak of 45C, the phone was warm, but not uncomfortable to hold, need to measure the surface temps next time. It had rock solid 60FPS all the way through and no throttling. All the games i play arent throttling at all on max FPS and graphics (Wild Rift, MLBB, CODm, PUBGm, ect ect)

It's not surprising, Xiaomi (and Poco) starts to be more secretive this year.

Kernel source is not being posted regularly, last was 3 months ago with many missing models.
MIUI 13 is not so different than MIUI 12, and it's already 1 year gap. They just claiming under the hood improvements.

They less, and less care about the software and start spitting hardware without concise support.