When you use this mode with easy placement mode, messages starts to spam your screen, is there a way to remove them yet ?

Currently still only in 1.12.2. But usually you shouldn't get that message almost at all, if you use the easyPlaceHoldEnabled option and just hold down right click. It would only get spammed if you spam click or use a clicking script/tweak, which is not how the Easy Place mode is supposed to be used.

I use the easyplacement mode and the placement restriction one at the same time

Easy Place uses placement restriction internally anyway, you don't need the placement restriction feature enabled separately for it.

The Placement Restriction feature is mostly provided as an alternative if you just want to avoid placing the wrong block, but don't want to use the arguably more cheaty full Easy Place mode, which allows placing against the schematic and also does automatic block orientation (to some extent).

So I'd recommend just enabling the easy place mode, and the hold option, and set the easyPlaceActivation hotkey to NONE with Allow Empty Keybind enabled. Then you just need to right click and hold and look at the schematic blocks to place them.

Ok thanks you for the support, but I can still place slabs on top of others (top slabs), and my building is only composed of them...

Slabs are pretty annoying in how they work in code. I fully rewrote the Easy Place mode in 1.12.2 over a year ago, and that new version works properly with slabs as well. It just hasn't been ported to any of the 1.13.2+ versions yet.

That's wierd because i added jack'o lanterns along with my slabs for my platforms and easy mode prevent me from putting slabs on other slabs this time