Drupal Core provides Vertical Tabs as Render Element: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Render%21...
So you would expect that if there are vertical tabs, there should also be horizontal tabs.
But that's not the case!
See https://api.drupal.org/api/drupal/namespace/Drupal%21Core%21Render%21Ele...
Try switching from
'#type' => 'vertical_tabs'
to
'#type' => 'horizontal_tabs'
and wonder horizontal_tabs isn't existing
Move the horizontal tabs implementation (and maybe also other field group types) from Field Group module → into core and remove it from field_group. Also deprecate Horizontal Tabs → module
Take advantage of vertical tab, add horizontal tabs into core.
Active
Idea
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FYI: horizontal_tabs are not only part of horizontal_tabs module, but also field_group module!
I created an issue in horizontal_tabs to deprecate it and join efforts on field_group module:
📌
Deprecate in favor of Field Group module
Fixed
Updating the issue summary.