Completely redirect website (with 301 redirect?)

You can place a simple redirect directive in the .htaccess file that’s in the root WordPress folder of the old site. In the .htaccess file that’s in the public_html folder on your hosting account (assuming that’s the root WordPress folder) put the following directive:

Redirect / https://newdomain.com

Hope this helps.

It does help, thank you a lot ??
Now, 2 more linked questions lol

1)Old website is in the public_html, but the new site will be placed in the public_html/newsite. Will this still work?
2)What about SEO, will this redirection have any affect on the rankings?

Once again, thanks a bunch

If you place the new website in a subfolder you should reflect that in the destination URL of the redirect command, so that the URL corresponds to the location of the new site on your hosting account. Using your example, the command should be:

Redirect / https://newdomain.com/newsite

Regarding SEO, by default the redirect is a temporary one (302 HTTP status code). With temporary redirects page ranking is not passed from the old to the new page. While with a permanent redirect (301 HTTP status code) the page rank is passed to the new page(s); some page ranking percentage may be lost though. So if you don’t plan to go back to the old site/domain you should use a permanent redirect. To do this put the status code right after the directive:

Redirect 301 / https://newdomain.com/newsite

Hope this helps.