[jpetso]

The Steam client has to restart in order to pick up the newly added external titles, at least last time I tried. In gaming mode, restarting the client means restarting the system, which is ever so slightly annoying.

Apart from that though, it works just fine on the Steam Deck.

[citrusybread]

I just tried it today actually - I just had to exit the steam deck UI mode, enter desktop mode, add them with Heroic, and then restart the deck UI mode from the desktop shortcut and it worked!