I am not sure I understood your question: are you connecting from Windows to a VNC server running on Mint? If so, the command you need is:
sudo ufw allow 5901/tcp
on Mint. This assumes that the port you are using is 5901. If the above command does not work, it means you are using a different port. To identify the port, issue the command:
sudo ss -lntp | grep vnc
You will get an output like:
LISTEN 0 5 *:5903 *:* users:(("Xtightvnc",17136,3))
from which you see that the listening port if 5903. Modify the ufw command accordingly.