Here you will find tutorials on how to connect your Recalbox to a CRT monitor.
Here are the available tutorials:
CRT Scart and VGA on Raspberry Pi 4 / 400 / 3
Configure your cathodic screen on DPI bus (VGA666 / PiScart / RGBPi)
Connect your Recalbox to a CRT screen using HDMI output
Connect your Recalbox to a CRT screen with composite
Connect your Recalbox to a cathodic screen with HDMI and SCART