clash detection

Assuming that's a default mitered connection and not s true overlap, there shouldn't be a clash.   Does your Rules tab have the default suppression rules checked similar to the attached image?

yes it is similar , and still I got clash

yes it is similar , and still I got clash

If there are any differences, can you attach a screen capture of the rules that are currently enabled?

OK, they do appear to be identical.

I would first suggest using the Connect Forms As L (Bisector) tool on those two walls, just to be sure that the joint does not contain any overlapping geometry.   Based on the image alone that's the only thing I can think of.

i used that one to solve the problem but it is not the default one , how I can make it default

But that is not a viable solution as a mitered cut is proper for unification and centerlines.