Thanks for the tips.
However, I did go to the developers' websites for both ONYX and PATHFINDER. I checked for "latest update" - dowloaded and installed, as usual. Then, I re-checked for latest update, and was told I have the latest version of both.
The "newest" version of Onyx crashes and Pathfinder will not even open in "High Sierra." For Pathfinder, the dropdown menu shows at launch, but the options are "greyed out" and the application can only be closed using Force Quit. Too much fiddling about in MacOS 13; no issues whatsoever with either application using MacOS 12.
I haven't entirely given up in OS13, but will wait a while to see if there is a bug fix update before trying again.
P.S. I usually do not update as soon as a new OS is released. This time I went against habit and upgraded too soon.