You can safely mount a dashcam on a tinted (rear) window, although visibility will of course be less than with a non-tinted window. The camera basically sees the same as you through the window, so if you can still see through it, so can the dashcam.
The quality of the image depends mainly on the image sensor and chipset used in the dashcam. With a blinded rear window, the image will naturally be a lot darker, so it can be useful to use a dashcam that performs especially well in the dark. You can see on our website at the specifications of each dashcam whether it performs well in the dark.
Still need help? Contact our support team and include your order number (if applicable), dashcam brand/model, and a photo/video of the issue.