@Pyper Hello, I think I have found the solution to this problem, I hope it helps you; The system runs slow because it takes a high resolution from your TV or monitor. When starting my reclabox it always defaulted to 4K, so the system was slow when entering the console menu. I found in the raspberry forum the following code that you must write at the end of the line in the cmdline.txt file of the "recalbox" partition on your SD:
video=HDMI-A-1:1920x1080i

This line will force Recalbox to enter the resolution you want when starting the system; you can even lower the resolution if you need it.