Find for each point-feature in layer the nearest point in other point-ayer over a network

I’m looking for a solution for following problem:

• given a point layer A (10.000 points)
• given a point layer B (15.000 points)
• given a line layer C, as network (waternetwork)

I want to have for each point in layer A the nearest point from layer B. That nearest distance must be counted over a network, layer C, and put in a new attribute column in layer A.

I have found some ideas using QNEAT3, but it processes the distances from all points from A to all points from B, which is a huge overload.

Thanks for replies.