When retopologizing weight-painted 3D models as a hobbyist, use tools that transfer existing vertex weights to the new topology to preserve deformation.
Hobbyist-friendly software like Blender has a "Transfer Vertex Groups" feature to map weights from the original model to the retopologized one; auto-retopology tools (e.g., ZRemesher, Instant Meshes) also help retain weight data. After retopology, check for inconsistent weights (gaps, sharp edges) in weight paint mode and smooth them with soft brushes.
If you’re new, start with simple models (e.g., a character’s arm) to practice—use Blender’s real-time preview in Weight Paint mode to tweak deformations as you go.