To get the Atari ST onto a modern monitor, I use RGB-to-VGA adapters. I have three of them: a passive MCSWITCH adapter on the "Low" machine, a self-built adapter on the "High" machine, and a newer active ST2VGA Enhanced that isn't in use yet.
The Mega ST 4 "Low" uses an MCSWITCH adapter (ATARI Monochrome & Color VGA Adapter) by Olivier Gossuin. It shows all three ST resolutions on a suitable VGA monitor, with a switch for mono and color, an A/V connector, and volume buttons. It's documented on albersdoerfer.de.
+The Mega ST 4 "Low" uses an MCSWITCH adapter (ATARI Monochrome & Color VGA Adapter) by Olivier Gossuin. It shows all three ST resolutions on a suitable VGA monitor, with a switch for mono and color. The version documented on albersdoerfer.de also has an A/V connector and volume buttons, but mine is an older revision without the volume buttons and with a slightly different look. I can't find my exact version at Olivier's anymore, nor a newer one, so the adapter I have is a bit of a rare older revision.
The Mega ST 4 "High" uses a self-built adapter. I followed the guide at pest.atari.org to build a simple RGB-to-VGA adapter for the Atari monitor port.