Every civ and city state needs to have a starting location.Do not modify or remove the "Free cities" entry, if there is one (depends on the ruleset).Selecting a specific Player civ will still allow selecting a random civ instead in the new game setup.I assume this is a bug, since it clearly worked before.
The option "Any" cannot be selected for the player for some reason it switches to "Random" automatically.Also set the amount of players and city states to values supported by the map.Set up a new game, and select the map in the map selection.Create the map in the builder (do not forget to give it a name to recognize it by).
#Civ 6 world builder guide mods
Save it as-is, then try to start a new game with it - if it loads without errors, you will be fine using those mods in the World Builder. Do not make any actual changes to the map. To test your mods selection, create a duel map in the World Builder (will load faster that way). In my tests, some of the map-related scripts caused errors, as well as startup scripts ( Expanded Initial Vision for example). This is because some of the information they expect to be present is not always available in a custom map.