Would be great if you add a hint here https://www.textasticapp.com/v8/manual/integration_other_apps/git_client_working_copy.html#use-drag-and-drop-on-ipad-to-open-a-repository :-)

After

• enabling Allow URL actions in Working Copy 
• adding Working Copy to storage locations in Files
• close and open Textastic

it works now. But please make this a better experience.

No, don't works for me on iPad Air 2019 with iPad OS Beta 7 

Nope, this doesn’t work with iPad OS Beta 7.