Empty pixels in polygon border

I have a vector shape file with the basins of South Carolina. Some of the sub-basins polygons have a "hole" or no data pixel in their boundary (See photos for reference 2) and I need them to be joined to the corresponding adjacent sub-basin. I’ve tried using Delete Holes, v.clean from grass, Fix Geometries without any luck. I’m using QGIS 3.14.

I also thought about rasterizing the layer, but the problem is that I will also attribute a value to all the ND values that are outside the state. I could do it by hand but this would take forever, wanted to find a more efficient way.