Most of this is used when the textures are not baked as a single instance. Most of the time, you’ll receive a UV passed properly baked but it might happen that because of multiple UDIMs it becomes difficult to manage the rendered UV pass.
Our solution to this is to use the normals (that are not split into UDIMs) and generate our own UVs. You can use this blink script to convert normals to to UV and then use those perfect new UVs to to texture/reflexion work.
BlinkScript Code to convert Normals to UV
I have to admit I am not the one to come up with this solution and this is a derivative of expressions I saw someone wrote on Youtube.
Here is this original video :
This blink script is basically a combination of all expressions and will allow you to use the GPU acceleration. Feel free to steal those super big brain maths ༼ つ ◕_◕ ༽つ