I am seeing the same behavior running the Spotify client on Gnome on Arch; the drop down menu items are all non-responsive.
└─[0] <git:(master 9df5b2511650) > flatpak list
Name Application ID Version Branch Origin Installation
Spotify com.spotify.Client 1.1.55.498.gf9a83c60 stable flathub system
Freedesktop Platform org.freedesktop.Platform 18.08.39 18.08 flathub system
Freedesktop Platform org.freedesktop.Platform 20.08.6 20.08 flathub system
default org.freedesktop.Platform.GL.default 20.08 flathub system
html5-codecs org.freedesktop.Platform.html5-codecs 18.08 flathub system
openh264 org.freedesktop.Platform.openh264 2.1.0 2.0 flathub system
Aurora xyz.kusma.aurora 1.0.0 master aurora-origin system
I remember researching this problem some months ago. The way to use the menu items is to put the mouse over them and click on Enter with the keyboard. I think it was Wayland related issue.