It might remind you of old PowerPoint presentations.
3D artist Binbun showed a cool transition shader made with Godot. You can apply your textures to it, and the result should be pretty and smooth. It uses gradient textures both for the direction of the transition and the shape of the edge.
"Most of the work in this went into stretching the UVs so that if you use a radial gradient it doesn't stretch. I made a very small tool script where the resize signal is connected to a function that passes in the size of the rect into the shader. Then in the shader I calculate the aspect ratio by dividing y/x of the rect size and scaling UV.y with that," the creator shared.
Binbun also has some nice VFX and materials on itch.io, which you can use in your own projects.