The OP’s problem was that transport operators do make that distinction, at least in Europe, and where multiple bus stops are located it’s probably worthwhile capturing that on OSM. Historically, there used to be separate bus stations for such services (Victoria Coach Station in London is one remaining example in UK; Estación Sur de Autobuses in Madrid another).

Actual tagging of the routes to distinguish them from regular “service buses” is a separate issue, but also one worthy of more discussion. If nothing else it would be nice if interregional services were shown on a lower zoom level on OPNV Karte & the Thunderforest Transport layer than they are at present.

PS. I rather suspect that Flixbus services on the Iberian Peninsula are not actually named in German (noted in passing).