The current (102.2.0) and at least the immediate prior versions of Thunderbird, are not dispalying any new mail notifications unless the lower right section of the screen is moused-over. The new mail sound does play, however. Both Cooker and Rolling, used Cooker Xfce ABF Build # 1308 to install, Rolling VBox was converted from Cooker.
Also reported as a bug: Thunderbird not displaying new email notifications unless lower right section of screen is moused-over · Issue #2847 · OpenMandrivaAssociation/distribution · GitHub