Time for an update on what has been done with the received donations, but not before I have thanked all of my supporters.
Since I accept donations (the day this thread started) I have received 66 cups of coffee from 21 supporters.
To everyone who has supported me, thank you very much!
Now regarding the spendings.
For the development of the Librespot Entrypoint I had a Spotify subscription for two months, a necessity to make it happen. As response is low I have cancelled the subscription for now.
And today I ordered a Raspberry Pi 4B 2GB. Not easy to get your hands on these days but there was a batch delivered to Kiwi Electronics (my tip of the day 
). When this is in I have a Pi2, Pi3 and Pi4 so a good set of boards for developing and testing Roon extensions.
As there will always be something next, the possibility to donate remains!
Thanks Guys!