Bilbao to Nantes by train or bus with a non-disassembled bike

Does anyone know an easy way to get from Bilbao to Nantes by bus or train with a bike that isn’t disassembled? Nothing on DB.DE, nothing on FlixBus... Thanks.

From Bilbao to Hendaye, it's local trains with space for non-disassembled bikes: Bilbao - Donostia, Donostia - Irun, then 2.5 km by bike — or maybe even direct to Hendaye.

And from Hendaye to Nantes, TER and IC trains also have space for bikes. Just make sure to book the necessary reservations — it varies by region and time of year, quite a mess.