Thanks for the screenshot, fmhsketch.
In the main menu> Render> Interactive render Region.
As a short cut, as mentioned above: option/alt+ R (Mouse over the editor view in question.
If this is not working at all, on the right side of that frame is a tiny little triangle, try to pull this down, which set the target quality. With that, the responsiveness of the system should be better.
Then try again option/alt+R (Again, the mouse must be over the editor view to make it work!)
If it is not working by now: Select all parts in the Object Manager and paste it into a new Project file. Alternative: call up a new project file, and merge the saved problem scene into the new one. That should take it out of the unwanted mode.
Worse case, I give you an upload link, and I will hopefully be able to send a working file back.
Fingers crossed.