To use Filter > Render > Tree..., make sure that you have a visible, regular layer selected. If you have a smart object, a layer mask, or an adjustment layer, then that filter will be grayed out. If you select a shape layer, the Tree filter won't be grayed out, but you'll get a message that you can't use it.
Whenever you edit colors and get the triangle with the exclamation mark, it means that you can't print the color with CMYK inks. Those colors are referred to as being "out of gamut."
Some filters require the use of your GPU. Make sure in your Photoshop's preferences Performance section that your machine's GPU is detected and ant that Use GPU is check. You need to have a GPU with at least 2GB of VRAN the ise supported by Photoshop.