This is likely a side-effect of this change:
https://github.com/discourse/discourse/pull/25764
The default value of this component setting should be a string (e.g., "0", or the type should integer).
However, it’s probably unintentional considering it returns a 500 error. Previously, it seems the value was converted to a string DEV: Centralise logic for validating a theme setting value by tgxworld · Pull Request #25764 · discourse/discourse · GitHub