Copy & paste between Windows and Mac when using VNC

I had the same issue with copy/paste using VNC Viewer from Windows to MacOS. It looks like you have to pay for VNC Server to get it working.

Instead I moved to Chrome Remote Desktop (so this doesn't answer the specific question, but is too long for comments). There seem to be two issues with this - one fixable and one not.

The issue I couldn't fix was that you will see a Window with "Your desktop is currently shared with...". I dragged this to the bottom right of the screen to hide it as much as possible, but you have to repeat this with every restart.

The second issue is that (obviously) the Windows key does not map to the Command key. This is "fixed" by choosing another key under "Configure key mappings". I chose to map ControlLeft to MetaLeft, and so then Ctl-C and Ctl-V (etc) worked fine.

Chrome Remote Desktop also solves one of your other issues - you can transfer files (although I have not used).