OBS does support multiple monitors. If there were general issues with that, you would see a huge number of posts about that issues, but there are none. The reports from a few months ago are from an update at that time that changed the internal behavior of how OBS selects a monitor for capture. In previous OBS versions, the monitor assignment wasn't persistent if you add or remove monitors while the system is running, that update addressed this. Every monitor selection became invalid with that update and the users had to re-select the monitor in the display capture properties. Some people didn't do this correctly, so they posted about that.
If you create a new display capture source on the current OBS, there are no such issues. You select the monitor your want to capture, and it's done.
Well, almost. It seems with certain hardware configurations, it's not possible to capture every monitor. Or the monitor that can be captured depends on the GPU OBS is running on. As far as I know, certain laptop hardware suffers from this. But this is how the hardware works, this isn't dependent on some OBS version.