you can try to convert the uri into a filename and try that filename with the activity starter... my file extension offers the method GetFileName for this https://puravidaapps.com/file.php
in case that method does not work for you (because actually it was created to Get path and filename from media content uri), you also can use the corresponding method from the filetools extension by @vknow360 https://community.kodular.io/t/filetools-some-tools-to-work-with-files/40051
probably it would be nice to have such method in the SAF extension directly?
btw. to simplify your blocks you can move all blocks from the Button2.Click event into the GotUri event...
Taifun