Not sure what the procedure for filing bugs is (having literally *hours* of experience under my belt now) but I think there's an issue with the dark/light mode on the Mac. At first I thought I'd lost the ability to render things in the render-window, but the button is there, along with all the other text, it's just white on white ...
My Mac is set to switch the background as the day goes on, based on time-zone, but I've quit/restarted Terragen - the rest of the interface is light-on-dark, but not the render window. Hope this helps, and if there's a better place to report bugs, let me know in a reply