JSON array of block content shown when trying to add

Problem/Motivation

Blocks are not added into the mega menu

Steps to reproduce

1. Add a column to hold a block
2. Pick any available block
3. Message is shown of JSON array of block content
4. Block is not rendered into column
5. As column is empty, config is not saved

Same issue is reported in https://www.drupal.org/project/tb_megamenu/issues/3471262 🐛 Custom or views block is not listed in blocks drop down Active (with another)

Drupal 11.0.4