

I went for this one and it works with both notify-send
and /dev/pts/0
. Not sure why it is better, but I opted for the latter. Simple, lightweight and versatile, suitable for any process.
Any KDE Plasma users reading this, to enable notifications history for these you can follow the instructions here. Many thanks everyone.
I have tried Syncthingtray and Syncthingy. I found the former did too much that I never used, and the latter was an unnecessary process doing very little while always running and adding another icon to the tray. For me periodic checking with a script is enough and more efficient for the rare situation where Syncthing crashes of fails to start.