@alessietto simplified you need to change your markup.
this is my first block type “tabgroup”:
<div class="tabgroup" id="<?php echo $block_id; ?>">
<InnerBlocks allowedBlocks="<?php echo esc_attr( wp_json_encode( array( 'tabitem' ) ) );?>" template="<?php echo esc_attr( wp_json_encode( array(array('tabitem')) ) );?>" />
</div>
this is my second block type “tabitem” which is a child of tab_group:
<div class="tabitem">
<InnerBlocks />
</div>
tabitem needs the json-key:
"parent" : ["tabgroup"]
or if you work oldschool with php array:
"parent" => array("tabgroup")
in the end you need to order the items and play with visibility via css like:
.tabwrapper { display:flex }
.tabitem { order: 0 }
.tabgroup { order: 1 }
check this article to understand the logic
