Problem with modifier shortcut remap

Like many of us I'm working from home at the moment and unfortunately I have to dial into work over Citrix to a windows environment. I have remapped most of the mac keyboard shortcuts I use to work on windows but I just cannot get CMD+Tab to work right. I was able to make this work on Karabiner, but that crashes randomly on Catalina.

In Citrix if I hold FN+CMD and press tab i see the windows app switcher. If I map CMD+TAB (when Citrix Viewer is active) to FN+CMD+TAB it switches the app but it doesn't leave the switcher visible on the screen while I'm still holding the CMD key. I've tried a bunch of stuff trying to solve this but haven't been able to.

Any tips or suggestions would be most welcome.