https://community.ricksteves.com/travel-forum/scotland/bus-fares-cap-at-2-in-shetland
This applies to all bus and coach services throughout the Highlands of Scotland and the Northern Isles- so the coach-bus from Oban to Inverness only costs £2, as does the coach-bus from Inverness to Scrabster Ferry Port (for Orkney).
On Shetland there has been some debate as to how it works, but the £2 fare should also apply to the integrated service from Lerwick to the top of Unst- 3 buses and 2 ferries.
All buses on Mull are only £2 as well (for instance Craignure to Iona)- so West Coast Motors have withdrawn their Mull bus rover ticket until 2027 as you can't use enough buses in a day to make it worthwhile.
On Orkney there may be circumstances where the weekly rover of £35.50 is still worth it, as that is only 3 buses a day on average.
Full Orkney timetable- https://www.orkney.gov.uk/media/e0vhtvq2/orkney-public-bus-guide-summer-2026.pdf