First of all, thank you for DISABLE_COPYRIGHT_FILES_DEPLOYMENT, it really saves the day!

Right now each library / executable is scanned running a separate dpkg -S. Then linuxdeploy checks for /usr/share/doc/PKG/copyright. This is extremely slow. dpkg -S actually supports multiple query paths in a single call, in case you want to batch the calls.

Another solution would be to add an --output-deployed-files FNAME to output the list of files for which the copyright files need to be found. After all, linuxdeploy has valuable logic to include / exclude deployed files from lookup.

I currently extract the AppImage created by linuxdeploy, list all .so libraries, look them up all at once in a single dpkg -S operation, and copy the results as appropriate. But mine is a simple case.

I've noticed that there already is a framework for deferred operations, so maybe that can be co-opted.