The regulations say:
The model rules do not contain a definition of the ‘rental of a means of transport’.
HMRC’s view is that a ‘means of transport’ includes any vehicle, whether or not motorised, and any other equipment or devices designed to transport goods or persons from one place to another, which might be pulled or drawn or pushed and which are normally designed and capable of being used for the transport of goods and persons.
The rental is not accompanied by the service for driving or operating the means of transport, which would instead be reportable as a personal service.
So, if you hire a boat to drive yourself, this comes under the rental of transport. However, if you rent a boat that comes with a driver who sails you around all day, that would be considered a personal service.
Essentially, if your app allows third party individuals or small businesses who own modes of transport to rent them out to platform users for a fee, then you are in scope.
If your app only facilitates the rental of modes of transport that are owned by your own company, then you are not in scope.