Baking Materials with multiple Slots

Before you start baking

The object has to be UV unwrapped in order to be able to bake
Cycles needs to be selected as your render engine
Go to the Shader Editor and Open the Sanctus Library Tab from the N panel (From the Shader Editor)

Baking Multiple Material Slots
For this guide I will be using a Suzzane with 2 material slots, one assigned to the head and one to the eyes:

We will start with Slot 1, as we would do with a single material

Select the Object, right click the Node Group of the Material you want to bake, click the “Select Sockets for Baking”

When clicked, select the Sockets to bake, then click OK

You will see your sockets added to the baking panel

Now we change to the next SLOT

Once you change SLOT, select the nodegroup from that material and you will see that a new button “Add Socket” appeared in the baking panel for each MAP

Click each of the Add Socket buttons and add the corresponding socket from the SLOT 2 material for each MAP, Color bake in Color, Roughness Bake in Roughness, and so on.

*If one of the materials has more baking sockets than the other (like an emission or displacement socket) you can leave that MAP with just 1 element, the baking tool will assign to the one that is missing a default value.

Adjust the baking resolution, samples and settings to your needs and click the Bake button. It will change to “Baking…” until the baking process is finished.
Once finished, you will see the textures in the Texture Sets ready to use.

You can now delete the slots and create a new material (Baked textures will not be deleted, they are linked to the object)
Once you created the new material, you will still see the baked textures in the baking panel.
Click the Instantiate PBR setup for a quick node setup ready to replace the procedural material