I tested this PR and it doesn't work for multiple selections

Yes, that's why it's working in progress (WIP). Any help to get this working would be much appreciated.

Blockly v12 node focus changes have a significant conflict with the nature of this plugin. Now I've made some patches to Blockly v12: google/blockly#9261

So that it can at least work with the plugin in this PR when you multiselect and drag the blocks, but I'm sure it's broken for many other behaviors for both Blockly itself and the plugin. I'll discuss this with the Blockly team to find out if there's a possible workaround.

Any news? @HollowMan6

Hi @TannerGabriel! You can find information on how to implement this properly at https://groups.google.com/g/blockly/c/7RSn9cXAulA. Unfortunately, I don't have bandwidth right now to work on this issue, but if you are interested, feel free to take over this PR/continue the discussion under that Google Groups thread.