I haven’t had to repair many iPhone XS Max but I recently had a customer with a broken front screen and back screen requiring a new lease on life. The front screen is no problem but I do not repair the back glass at this time. Here is a nice little work around though and my recommendation at this time. Even as an iPhone repair shop, my recommendation is to get a nice case that will cover the back screen. YouTube is full of videos of people replacing the back glass and it is no small feat.
Hope this helps
Photos coming soon.