Version 0.99.120.1-beta (WebKit 614.1.20)
MacBook Pro (macOS Monterey 12.6 build 21G115)
This is similar to a recently fixed issue. Drag and drop from the local file system to trigger an upload is fixed in slack per that issue, but in github.com's pull request compose boxes, Drag and Drop still takes over the entire tab rather than trigger the correct site specific drag and drop handling.
This can be reproduced with any github PR compose input box.