Hi,
> It is assumed that when I select a project the index.php should be opened by default, but it should not.
NO. It is assumed that when selecting a domain name, i.e. a VirtualHost, the index.php file must be opened by default.
By choosing to "launch" a folder (this is what you do when launching a project) there is no domain name or VirtualHost, so the DirectoryIndex directive cannot be applied.
I repeat the end of the answer of RiggsFolly:
See
The need for Virtual Host and
Wampserver 3 - Create or add a VirtualHost---------------------------------------------------------------
Documentation Apache -
Documentation PHP -
Documentation MySQL -
Wampserver install files & addons