Manually, you should probably be able to separate corner pieces from each of sides pieces .. imagine 3 x3 grid and you cut it up into 9 pieces with 4 corners, and then each 4 sides and a center.
In Godot use NinePatchRect and you input the # of pixels each corner is.
in Unity, you add Sprites package and setup a 9-slice sprite .. see youtube for tutorial ...
Idk other game engines right now...