Not quite sure where the problem starts, but the register_block_type call in Block.php does not actually register the block, which can be confirmed via wp.blocks.getBlockTypes()
The updated 6.8 now has the additional method register_block_type_from_metadata to register blocks, but designed when the project uses block.json and not an array.
However for a MB block using block.json, this method also is not working.
