Close vmware horizon client.
open terminal

vi /usr/share/applications/vmware-view.desktop

Exec=vmware-view %u

Change it to:

Exec=env GTK_THEME=Yaru-light vmware-view %u

save

Restart app and now you should be able to view everything properly.

If you don’t have Yaru-light as a theme you may need to change it to what ever your OS light theme is named.

EDIT:

System versions

Horizon Client version: 2111 / build: 8.4.0
KDE Neon / Ubuntu 20.04 Linux kernel 5.15.22-xanmod1
KDE Plasma 5.24.1
Qt Vesrion 5.13.3