So I have put some frames of an animation in a sprite sheet, cut them with the sprite editor.
And now I would like to use them in a shader, like a sequence of frames.
How do I do that?
What are you trying to achieve? If it’s just a sprite animation, using a 2D texture and changing the UVs is a tried-and-true technique that is part of Unity 2D right out of the box, avoids filtering issues, and lets you pack more onto a single texture. Slices of a 3D texture are used when you want to interpolate smoothly between the slices, eg a burning fire.
I have a bunch of frames of the boiling surface of the Sun, and I want to use them on a sphere to make… the boiling surface of a star 
This requires to have the sprite slices used not as single instances over a quad, but as slices of texture repeated on the UVs.
But in reality, I already know the answer: you need to write a custom shader that gets the UV coordinates from the texture frame by frame, increasing by .125 on X each frame and then by .125 on Y each 8 frames…
Unluckily, I chose to stay on the Built-in graphics pipeline, for many reasons, so no shader graph for me… and don’t tell me to code it, I can’t 