I have now 2 rwmb_meta_boxes added to a settingspage with two tabs.
Instead of tabs I will use a top-level menu page and 2 sub settings pages.
I have add two sub settings paged, it works.
When I change the meta boxes from settings page top to the subsettings page AND remove the tab then the MetaBox shows in the sub settings but all the fields are empty.
The top and sub-settings pages have their own option names and save field values to the database in different rows. So the field values will not be displayed when you move the custom fields from the top settings page to the sub-settings page.
If you use the builder or code to change the settings page of a field group/meta box, the custom fields will not display on the old settings page but the setting value is still available in the database until you delete it (like post meta).
You can access your database and delete the old setting value manually.
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