There is no true difference.
In general, foreigners will have worse or slightly off handwriting. However this is because of less time practicing writing chinese by hand, or not learning proper techniques. You will also see natives who haven't had as much writing practice or learned improper techniques. These people with poor writing are indistinguishable as foreigner or native-- they are all equally "incorrect" or "lacking practice". Think of any native english speaker you know with not beautiful or even straight up illegible handwriting-- it can happen to anyone.
In the same way, there are plenty of foreigners who have put in the time to practice handwriting and learned proper techniques. There handwriting will be indistinguishable from a natives, maybe even above average if its nice and legible.
At the end of the day, writing is its own skill, seperate from ability to read or speak or other language abilities. Consider that everyday, our modern world moves more and more to typing, making writing less and less important. This lowers everyone's handwriting ability, and the lines become blurrier and blurrier everyday (literally lol).
Even so, anyone willing to put in the hundreds of hours of practice can achieve calligraphy level beautiful handwriting-- english or chinese, native or foreigner(･̑◡･̑)