Bug: Nextcloud Password Client installed from Flathub won't pin to Task Manager in Plasma 6 on Deb 13

I figure it is probably happening on other versions of Plasma and possibly on other Desktops, but here are all my versions:

Debian GNU/Linux 13.1 KDE Plasma 6.3.6 KDE Frameworks 6.13.0 QT Version 6.8.2 Kernel Version 6.12.43+deb13-amd64 Graphics Platform X11

I installed Nextcloud Password Client on a fresh system using Flathub and I found that I couldn't pin the app icon to my Task Manager. After a lot of digging and fiddling I discovered the fix. The .desktop file at /var/lib/flatpak/app/com.gitlab.j0chn.nextcloud_password_client/current/active/export/share/applications/com.gitlab.j0chn.nextcloud_password_client.desktop (linked by /var/lib/flatpak/exports/share/applications/com.gitlab.j0chn.nextcloud_password_client.desktop) just needs one line added to the main section.

StartupWMClass=Nextcloud_password_client

This resolves the bug.