The Access Code says:
Access rights apply to everyone, including people with a disability. Access rights extend to being on or crossing land in a motorised vehicle or vessel which has been constructed or adapted for use by a person with a disability and which is being used by that person. Follow the Highway Code at all times. If you are using such a vehicle or vessel, take care to avoid disturbing animals or wildlife, and respect the needs of other people exercising access rights and the needs of land managers.
The Phototrails website provides photos and information to help you discover and enjoy access to the countryside, tailored to your own needs and preferences.
The Forestry Commission Scotland website provides information on accessible routes. Choose an area or town and click on ‘filter by activity’ and then select ‘easy-access trails’.