That's awesome you got the texture mods working for Final Fantasy IX remaster! Unfortunately, the remaster itself doesn't offer a built-in option for a 16:9 aspect ratio. The game runs in its original 4:3 format with black bars on the sides to fill widescreen monitors.
While the texture mods you installed likely work fine with 4:3, there aren't any official widescreen compatibility mods out there. This is because stretching the 4:3 backgrounds to 16:9 can cause graphical glitches and distort the art style.
Some people online have experimented with unofficial widescreen mods, but these can be buggy and may not work perfectly throughout the entire game. It's best to stick with the intended 4:3 aspect ratio for the most stable experience.
Enjoying the remaster with the texture mods is a great way to experience the game with a visual refresh!