Thanks for the reply, all the themes I have were installed from the following apt packages:
root@sr66-thelio:~# apt list | grep -e installed | grep -e theme
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
adwaita-icon-theme/noble,noble,now 46.0-1 all [installed,automatic]
gnome-accessibility-themes/noble,noble,now 3.28-2ubuntu5 all [installed,automatic]
gnome-themes-extra-data/noble,noble,now 3.28-2ubuntu5 all [installed,automatic]
gnome-themes-extra/noble,now 3.28-2ubuntu5 amd64 [installed,automatic]
hicolor-icon-theme/noble,noble,now 0.17-2 all [installed,automatic]
humanity-icon-theme/noble,noble,now 0.6.16 all [installed,automatic]
mate-icon-theme/noble,noble,now 1.26.0-1 all [installed,automatic]
mate-themes/noble,noble,now 3.22.24-1 all [installed]
plymouth-theme-ubuntu-mate-logo/noble,noble,now 24.04.0 all [installed,automatic]
plymouth-theme-ubuntu-mate-text/noble,noble,now 24.04.0 all [installed,automatic]
plymouth-theme-ubuntu-text/noble,now 24.004.60-1ubuntu7 amd64 [installed,automatic]
qt5-gtk-platformtheme/noble,now 5.15.13+dfsg-1ubuntu1 amd64 [installed,automatic]
qt5-gtk2-platformtheme/noble,now 5.0.0+git23.g335dbec-6build5 amd64 [installed,automatic]
qt5-xdgdesktopportal-platformtheme/noble,now 5.15.13+dfsg-1ubuntu1 amd64 [installed,automatic]
qt6-gtk-platformtheme/noble,now 6.4.2+dfsg-21.1build5 amd64 [installed,automatic]
sound-theme-freedesktop/noble,noble,now 0.8-2ubuntu1 all [installed,automatic]
ubuntu-mate-icon-themes/noble,noble,now 24.04.0 all [installed,automatic]
ubuntu-mate-themes/noble,noble,now 24.04.0 all [installed,automatic]
yaru-theme-gtk/noble,noble,now 24.04.2-0ubuntu1 all [installed,automatic]
yaru-theme-icon/noble,noble,now 24.04.2-0ubuntu1 all [installed,automatic]
yaru-theme-sound/noble,noble,now 24.04.2-0ubuntu1 all [installed,automatic]
yaru-theme-unity/noble,noble,now 24.04.2-0ubuntu1 all [installed,automatic]
Now as to which of those the theme came from, I'm not sure. I've done some apt-file searching but don't have anything yet. I'll have to dig more.