If you want to link a new domain to serve the content from the subdomain, instead of adding a subdomain, link the new domain as Addon Domain. Addon Domains section is available if you’re using cPanel. Check with your web host whether your package supports Addon Domains. Sometimes you might need to upgrade your hosting package to get this.

If you intend to use the subdomain https://soielin.severineautin.com, remove the .htaccess file you have created. Then try accessing the site.

Let me know whether the above step solves the problem.

Good day!