Spigen Neo Film (2-pack)
Another option to protect your Galaxy S9+ screen is the Spigen Neo Flex. This is a durable film, and you get two, and not a tempered glass protector. However, some prefer a film as they're easier to install.
If you've had trouble with tempered glass on curved screens, this is a perfect alternative. Spigen's NeoFlex film is a military-grade 3M film that's extremely durable. They recommend installing it with the case already on your phone. That way it fits perfectly. This film won't have any weird textures, no rainbow effects, and won't discolor or yellow over time.
The wet installation method ensures you won't have any bubbles on the screen once you're done either, so that's a plus. Oh, and if you run into problems you get two, so you can try again. Otherwise, give the second protector to a friend, family member, or save it as a backup.