RewriteRule hidden file extension problem...

#RewriteRule ^([^./]+)/?$ $1.php [L]

I have a website, let’s say it’s called xxx.com, and the directory where it’s stored is called xxx
The FTP path is
home2/*/public_html/xxx/

Since I did not use #RewriteRule ^([^./]+)/?$ $1.php [L]
so when I added another main website (home2/*/public_html/) After this code, when I enter xxx.com, it will become 404. I must add index.php to make it normal. This is equivalent to him automatically adding my xxx to this code... But I did not use this code in xxx.
So he read xxx.com into xxx.com/index, so it will get 404
How can I change this RewriteRule? Do not affect other directories!

My current approach is to add
RewriteRule ^index$ index.php [L]

My only website does not have hidden attachments My name is xxx, so it happened suddenly... I didn’t expect it to happen