500 internal error in each post

RewriteBase /main.domain.it/

Your RewriteBase should be /.

main –> /main.domain.it
sub1 –> /main.domain.it
sub2 –> /main.domain.it
(using “parking” all is redirect to https://www.domain.it)

There is something wrong with the your webserver parking or DNS. You should be parking the domains. Do not set up a redirect in the configuration of the domain at either the webserver or DNS.

Ok, now my configuration is :

the server (with cpanel) with this subdomain and path:
* –> /www (but without this, the result is the same)
main –> /main.domain.it

parking domain (with cpanel)
sub1.domain.it –> /
sub2.domain.it –> /

.htaccess in /main.domain.it path is as wp write in network configuration ( with RewriteBase / )
.htaccess in /www is untouched (but if is as wp write in network configuration, it is the same)

no change in wp configuration

now :
https://www.domain.it go to https://www.domain.it
main.domain.it go to main.domain.it
sub1.main.domain.it go to https://www.domain.it
sub2.main.domain.it go to https://www.domain.it
sub1.domain.it go to https://www.domain.it
sub1.domain.it go to https://www.domain.it

Have you any idea?

.htaccess in /main.domain.it path is as wp write in network configuration ( with RewriteBase / )
.htaccess in /www is untouched (but if is as wp write in network configuration, it is the same)

Do you have 2 WP installs or just one?

If it’s 2, then which one are you domain mapping in?

If it’s only 1 then you should only have one .htaccess.

I have got 2 WP install :

1 at https://www.domain.it as simple install
1 at main.domain.it as multisite install

In that case the following should not be happening

(else all is redirect to https://www.domain.it)

There is something wrong in your web server configuration. After you parked the domains did you restart Apache? (cPanel sometimes fails to restart Apache after configuration changes).