I hadn't played the game in a few months, so I initially thought this was just related to mods, and removed them. Now I see from other threads this is a recurring problem.
I can create a game *with* mods if I do not enable caves. But I cannot create a game with caves enabled, mods or not. If I try, I get the error in the title. It also does not create any game at all in the "Host a Game" list that would be selectable. So I'm not sure if it even makes a cluster folder. But based on time stamps, the attached Cave and Master server logs may be the correct ones. I have also attached the client_log from "C:\Users\Brian\Documents\Klei\DoNotStarveTogether".
I saw responses related to "read access" issues. I have no issues actually doing anything in any of my folders. However, all folders on my computer, when properties are selected, show the "Read-only" box checked. Unchecking it and clicking OK appears to change it. But when selecting "Properties" again, it's checked again when that menu is opened in Windows File Explorer. I've tried to use this site's advice on how to resolve that, and none of these work, some because my screens don't even have the same options available.
Select Host a game