Show a block on the user registration form depending on destination parameter
As @runswithscissors pointed out this module does the trick Block Conditional Visibility by URI Query Parameters Thank you!

Step 1

Download and enable drush en block_query

Step 2

Go to blocks admin/structure/block and create a block or enable one of your choice. There are no specific configurations elsewhere. It's a very lightweight feature.

Step 3

At the page of your block, under the "Visibility settings" you will now see "Queries" to "show block on specific pages", add the query parameter ONLY. 
E.g. if you have a destination parameter that leads to that particular page, only add the part behind the question mark ?, not the entire path. 

Test it out

Let us know if it worked for you too.