Problem to bake different materials / objects on a new grouped uv map

Hello, I would like to bake my textures from different materials on a single map to limit the number of textures.
I found this tutorial from Grant Abbitt https://youtu.be/9airvjDaVh4?t=3 it works fine for the base color but when I try for the normal map I have a problem.
So I have 2 uv map, The first “UVmap” by default on which my textures are placed and the second “joined” that I added after having grouped the objects and which will be used to place my new grouped texture.
The problem is that when I activate the 2nd uv map the relief of the wood that I have baked from a high poly version is inverted … the hollows become bumps. I’m sure I can find a solution to artificially reverse the normal map but I would like to understand what I’m doing wrong.
What is curious is that the metal rings do not have any problems even though I do exactly the same thing

Edit: I found a way to reverse the normal map with the rgb curve but that doesn’t solve the problem. I don’t understand anything, it reverses the relief on the sides of my barrel well but on the cover above it looks strange. .
There are also other weird problems, some parts of the wood look brighter (a problem that I have seen before when there is a problem with the normal map)

Ok … I think I misunderstood how to proceed for the other maps … I think I understood that in reality I should not use the normal-map bake with the normal channel but all the time the base color channel, as if normal was just a color texture like any other.
I haven’t tested yet but there is no reason that it doesn’t work.