>>1017421
my guess is the normals are flipped the wrong way. If you're in edit mode you can select all and hit alt+N shift+N which will open the normals menu then recalculate outside. Pic related if you're ever curious if your normals are facing the right way amd the statistics button in there is useful too. As for retopology there's a million ways to do it yourself and that paid quad remesh addon is the easiest "make my geometry better" button available. It's not perfect though and for character modelling you'll probably always need to do a bit of topology cleanup for animation ready deform capability