Use APKPure App
Get Resource Monitor Mini old version APK for Android
Check Available Resource: RAM / CPU loading / frequency / temperature
This is a mini resource monitor. It monitors available memory and CPU loading. It will always stay in the corner of your phone's screen.
Set the overlay to any corners of the screen, customize the color and transparency.
(CPU loading is an estimation for newer device)
Pro version:
https://play.google.com/store/apps/details?id=info.kfsoft.android.MemoryIndicatorPro