I know that you (obviously) can't take a pc graphics card and put it in your laptop, but are you able to exchange graphics cards between laptops (i.e. take a graphics card from one laptop and put it in another laptop)
It depends, if the make and model is similar, ( from a high end sku to a low end sku ) likely it’s going to work.
Cross brand I don’t think so as the form factor of pcb and cooling solution could be slightly different, certain laptop has improved power delivery for higher end video card as well, so ymmv. Generally no.