- Issue created by @skyriter
I tried to reproduce the error locally, and it seems that the root cause is not in the Allow Only One module but rather in the Markdown module.
More specifically, the issue comes from its CommonMark plugin, which was calling a deprecated method setConfig() from the league/commonmark library. This method was removed in version 2.3, which caused the WSOD (White Screen of Death) when accessing the help page.
Here's the thread https://www.drupal.org/project/markdown/issues/3419098 π Call to undefined method League\CommonMark\Environment\Environment::setConfig() Needs review .