I tried the method where you put the custom block in your backpack, remove the custom block definition, go to another project, and place it in the other project, but it still appeared as a normal custom block. I searched for projects that claimed to have undefined blocks, but they were just random blocks. Loading them in the Scratch 2 editor shows the undefined blocks though.

So…were undefined blocks removed?

I think so. The closest thing there is to an undefined block is a red hacked block that's both a hat and cap block. It looks like this

Col_Cat228 wrote:

I think so. The closest thing there is to an undefined block is a red hacked block that's both a hat and cap block. It looks like this

The red hat block is 3.0's undefined block, which shows up for all invalid blocks.

i saw the same thing one time, but i never saw the unidentified block.

No, Red Blocks (AKA Red Hat Blocks) can still be found.

to get that block, type %15 in search bar, then enter. copy the symbol  and go to editor. scroll to my blocks and click create block and paste the  symbol in. when you click OK, you'll see the red block.