Below are two short videos to show you how you can find the best and most convenient flights.
There are no direct flights from London to Olbia until end of March 2022. There are direct flights from London to Cagliari though, and Cagliari is definitely worth a visit.
Stay overnight, have an evening and a morning in this beautiful town .. here is a nice b&b I stayed in before – perfectly central and cheap.
then take a train up to Olbia – 3 and a half hours train ride, € 18.
Silvia might be able to pick you up in Olbia.
Here is a short video in case you are not so familiar with how to find the best flights on Skyscanner: https://www.loom.com/share/e5ee09c5630442c3b5eed2191a48eb64
and here is another bit https://www.loom.com/share/596d2e7002b84163b857ed11c2ed7caa