To confirm, are these the steps you've taken? Just double checking!
Import the new_matter_claim query from the query library & into your app
Replace {{uuid_var}} in the imported query with {uuid_var: '123456'}. Run & confirm it works.
Add {{uuid_var}} back into the imported query and add a JS query: new_matter_claim.trigger({additionalScope: {uuid_var: '123456'}})
Run the JS query & see that the imported query is successfully triggered
Check db and see that it was not actually successful
Could you let us know your version number as well? The version info can be found by clicking on the chat icon in the lower right corner of your screen. A menu should pop up which will show your Retool version number: