Hi trecile, I took the bus from Pamplona to Bayonne after I finished walking the Aragones in 2019. I didn't remember changing bus but it did stopped at a few places, and the stop at Bayonne is close to old town and the cathedral -- but it was just a stop at the street not a bus terminal (so be aware, but things could change)! Also the bus ticket would show "Bai'on" or something, I thought she sold me the wrong destination, but the kind lady at the Pamplona bus office assured me that it is Bayonne, just slightly different spelling in French!
I also stayed at Chez Veronique, very close to the cathedral Bayonne. Enjoyed walking to Biarritz but easy to get lost -- almost wind up in St Juan de Luz! and also took the local bus back, easy and enjoyable!
I took blablacar once in France, we were glad that the driver was so kind and speak English, enjoyable experience! They only stop at designated spot but good thing Bayonne is not big!
After couple days in Bayonne, I took the flixbus to Bordeaux for my flight home, but flixbus was late for three hours due to mechanical problem (they did texted me), the replacement bus was not even marked (and not texted me) -- I would have missed it if not for asking the bus driver!
Buen Camino!