why here when l come to extrude manifold the bevel modifier got spoiled
..... by the ay l have the scale applied firstly
..... thanks in advance 
Hi Ahmed,
That's a great question and I wrote an extensive answer, but then my answer was lost, because I was mistaken for a bot😉
Let's try this again. I've never seen anybody so brave as to use Extrude Manifold together with a Bevel Modifier.
The truth is, that Extrude Manifold is a bit of a hack and can be somewhat buggy at times. I don't know how it works exactly and why it seems to break the Bevel Modifier (it doesn't appear to create double Vertices), but as mentioned above, disabling Clamp Overlap should fix it.
this is not belong to my braveness pal .... this belong to my noobness ...... is noobness a correct word ?? ldk ....... #_#
Well, apparenlty, I am also still a noob, when it comes to the Bevel Modifier (after more than 13 years of using Blender almost daily); I did some tests and these 3 'cubes' all have the same shape and the same Bevel Modifier (Clamp Overlap enabled) and I don't know why the middle one won't Bevel:
