Thank you @Tuba

After all these years, how could I not think to run it in a terminal 🤦‍♂️

I installed it as a snap.

The error output includes,
"SecretAccountStore.vala:46: Error while searching for items in the secret service: An AppArmor policy prevents this sender from sending this message to this recipient;"

Rather than digging into the snap AppArmor profiles and trying to find the right bit to correct, I have installed flatpak and will try installing Tuba from there...