Created slideshow and audio in Photoshop Elements 11 on old computer. Now Photoshop & Premiere Elements 2019 are installed on a newer computer. Now want to use thumbdrive to move slideshow & associated files to new computer & edit.

New Elements versions are not compatible with slideshows in PSE 11.

You could reinstall PSE 11 on the new computer together with the 2019 version if you want to continue your project. PSE11 can be installed together with newer versions.

To recover all your assets, the recommended way is to use the organizer backup and restore process.

Move Elements Organizer catalog

Did you save your slideshow as a 'project' (.pse) in PSE11 ?