I want the remote Linux Mint Cinnamon 20 machine to AutoStart TeamViewer on boot
In TeamViewer go to Extras > Options and check the box next to "Start TeamViewer with system"/
Is the daemon started/enabled?
Try `sudo teamviewer daemon enable` then try again, maybe while installing the script didn't succeed enabling the service it need for remote connections.
What desktop environment are you using? Cinnamon, Matte or Gnome? Is it a wayland or Xorg session? If you are using wayland remoting into your machine is not supported, consider using Xorg if this is critical functionality for you.