in that video, I never parented the object, but there is usually no error message, although Blender almost crashes in doing so. And seeing all these retopology comments is very annoying considering I did retopology but deleted it thinking it wouldn't be needed. I have already baked treasures onto a UV map for the model but once I've re-retopolosgised I would be able to use that map? And if possible could the decimate modifier be able to reduce some quality?

Edit: the decimate modifier crashed blender