Sooo, I don't quite understand what you want to do. Acccording to
Brierley (2024 Camino Portugués) you can walk both sides of the Miño - Portugal and Spain as far as Vila Nova de Cerveira on the Portuguese side. There is a vehicle & pedestrian bridge - but there is no camino that continues east along the Spanish side. You CAN, however, walk on the Portugues side of the river to Valença, then just walk across the bridge to Tui...
I thought I saw - somewhere, yesterday, maybe on this forum - that there is a boat from Caminha to Valença. Buen Camino! And please post when you do this route!