The POCO F1 from Xiaomi took up the mantle of being the best affordable flagship, beating the likes of the OnePlus 6 and OnePlus 6T when it came to providing the best value for your money. Thanks to the Qualcomm Snapdragon 845 SoC, LPDDR4x RAM and UFS2.1 flash storage, the POCO F1 had all the ingredients for providing a good gaming experience through some solid heavy-hitting performance.
If you are looking to extend the same performance that you find on MIUI for games to custom ROMs, XDA Member dragneelfps‘s Thermal Config Changer lets you conveniently control the performance profiles on the device. The app lets you set the value of /sys/class/thermal/thermal_message/sconfig, which is changed automatically on MIUI but not on custom ROMs. The app requires root to function, but since the app is open source, you can verify what it does with those permissions.