A little more information:
I got a new computer, with Windows 11, about a month ago, and that is the one that has the problem with the missing Spherical camera setting.
I checked my old computer yesterday, and on that machine I can see the setting. I upgraded that computer to Windows 11 only a few days ago, so on the computer where the Spherical setting is present, I installed Terragen on Windows 10, and upgraded to Windows 11 after.
The new computer has a screen resolution of 2560x1440. I don't have access to the old computer right now. I'll check the resolution when I get back home.
One thing, I do not know if this is a bug or not: I am working on a scene with a planet seen from space. There are procedural stars in the background. When I rendered a 360 panorama on the old computer, all I got was a picture of the background stars. The planet was not visible.
I'll try doing a 360 panorama render closer to the ground this weekend.