Hello @Bright360F !
I think that it may be a problem with the material, but not every UI Widget has materials so you have to check it.
In the Widget Menu, in the Details Tab, can you search for “Material”?
By default all the images in the UI do not respond to the lights of the scene, but if they do it is usually because they are associated with a material.
If you find that it has a material, you just have to go to that material and make it “Unlit”.
Let me know if you need any more help.
I hope if this helps you!