htaccess directory ?

I think the answer is in your P.S.
WordPress is quite “allergic” to this kind of settings. (doesn’t your host let you create subdomain without redirecting?)
BTW, and what do you have in Options > General for the 2 URIs? Are they different?

i can create subdomains and on my hosting control panel
i should point subdomain url to folder at my root directory to make it work. or am i missing something here ? ??

my url settings are like this ;

WordPress address (URI): https://www.domain.com/blog
Blog address (URI): https://blog.domain.com

1. My subdomains stay the same, I don’t have to redirect:
https://subdomain.example.com/whatever.php or .html
(real life ex. https://crosscultural.transycan.net/ )

2. I am afraid (though not 100% sure) the 2 URIs “confuse” WP as to where to write the .htaccess file.

Solution is, your .htaccess file should include the following:

DirectoryIndex index.php index.htm index.html