Hey, I came across this post whilst updating my projetcs to the new block.json registering technique.
I followed all the advice above but still my block was not showing up. I ran my block.json file through a validator which tidied it up, corrected an erroneous quote mark and then it worked!
It seems if your block.json isn’t valid or has errors, it fails silently and you never know. So double check that json and hopefully that will also help.
