According to ny understanding, in most cases other than special exceptions, it is not possible for an airlines to carry domestic traffic of other countries, even if the airlines have traffic right for individual segments.
For example, an airlines from Canada can carry traffic between SEA-YYZ and YYZ-EWR, but it can’t sell transfer tickets to passengers going SEA-EWR to transfer via YYZ.
Likewise, an airlines in Singapore can carry traffic between KNO-SIN and SIN-SUB, but it won’t be able to carry traffic between KNO-SUB. (Medan, Indonesia and Surabaya, Indonesia)
Or, an airlines at Dubai can carry traffic between DXB-CDG and DXB-RUN (Reunion), but with Dubai not being part of EU, they wouldn’t be allowed to sell ticket to passengers going from CDG to RUN.
A relatively fanous example in this is probably Asiana being fined for selling tickets that carry passengers between Continential US and Guam.
It seems like the restriction is not modelled in the game according to search result in ORS.
I think that, even if not for cabotage right, most usual passengers probably won’t pick an international flight that require carrying passport and pass through border control, when they otherwise wouldn’t need to