New mail notifications in XFCE panel stopped working

[jt1122zz]

OS
Sparky Linux 6 (=Debian testing), XFCE desktop 4.16

Gmail Desktop Version
2.25.3

Describe the bug
The app shows a Gmail icon in the panel notification area.
Previously the icon would change once new emails have arrived.
This has stopped working, i.e. the icon remains unchanged even when new emails arrive.

Steps to reproduce the behavior

1. run gmail-desktop.
2. Send an email from another address.

Expected behavior
The GM icon should change once new emails have arrived.

Thanks