This is probably the best wireless keyboard and mouse combo according user reviews but sadly i can not connect via bluetooth.
https://www.logitech.com/en-us/products/combos/mx-keys-s-keyboard-mouse-combo.html
The phone finds it when i search bluetooth devices but when i click on it to connect immediately shows as disconnected.
Just comparison the very same keyboard set perfectly connects to a Graphene OS phone. So it is clearly OS related bug on fairphone 5.
It would be great to look into it as many people would love to use this phone with external display and keyboard.