@mitu Built SDL 2.0.14 with--disable-video-rpi --enable-video-kmsdrm
The FPS problem still exists with 5.4 kernel, or newer one after full SO upgrade (in this case with fkms or kms), and in this way when emulator is closed EmulationStation is frozen.
Anyway I found a solution, if VERTICAL SYNC is enabled also on emulator (I added a command line parameter for this) also Raspberry Pi v4 version is ok.
If you don't have any other idea I'll stop the investigation, I don't love VSYNC because if a user has a 50 Hz monitor all games with nominal 60 FPS framerate runs at 50 FPS.
Really appreciate your help