I've been searching multiple threads, but can't seem to figure out how to get alt + tab to work on Ubuntu 19.04 with the Citrix Workspace app/extension within Chromium (tried Chrome, too). There's also an HTML5 in-browser option available that launches my Citrix desktop, but this doesn't allow for alt + tab either.
i used tatsu's answer above. i reassigned the alt + tab shortcut to alt + ` under settings->devices->keyboard->shortcuts. works like a charm now in chromium :)