Thanks to Does Gnome3 have a method to filter desktop notifications? I logged dbus traffic to /org/freedesktop/Notifications
. Indeed after a while I found the culprit: it was a notification from Firefox.
$ dbus-monitor "interface='org.freedesktop.Notifications'" | tee ~/notifications.log
...
method call time=1664969078.354566 sender=:1.53 ...
path=/org/freedesktop/Notifications;
interface=org.freedesktop.Notifications;
member=Notify
string "Firefox"
uint32 0
string ""
string "Une berline à la personnalité affirmée"
string "Sponsored Content by Taboola"
array [
...
Opening the Firefox "Privacy and Security" settings, down in the the "Block pop-up windows -> Exceptions" menu, indeed somehow a Renault domain was in the Allow-list. No idea how it got there, I guess I'll never know. I must have pressed a wrong button.
Anyhow, I'm removing that domain and hope to never see the pop-ups again.