I suspect (based on similar issues years ago) that you could get it working on MacOS in either one of two ways:
1. Set a password for the setting “VNC viewers may control screen with password:” in the screen sharing settings. Most of the issue with standard VNC clients is that MacOS uses MacOS-specific login security, but setting a password opens it up to VNC-standard security
2. Install an alternate VNC server on the Mac. This bypasses all the MacOS security nonsense.
I don’t have personal experience, but for these types of low-level things, I start my research with `brew`. In this case it looks like https://formulae.brew.sh/formula/tiger-vnc is a contender.
https://github.com/matteodelabre/vnsee
The author is also very nice and responsive to bug reports.
I've managed to make it work as second monitor for linux virtual machine.
I wish I could use it as second monitor for Mac and was unable to make it work with MacOS so far.
Anyone made it work with Mac? Who knows how to make it work with MacOS ?