Resolved not exported SUBFORM (test on demo site)

Hi everyone,

On the demo site, I created a subform subform field for articles, but I had an error message in all attempts (error 200, error 500...), and I failed to output subform custom fields along with the site contents.

And of course, I noticed that the demo site is old, because in Joomla 5.2, the possibility of nesting is provided for the subform custom field...
(subform inside subform inside subform)

Is this bug only on the demo site? Or is there a special document for subform custom fields?
(My site only has news articles with a large number of custom fields that I need to update the fields)