Moving WordPress to the root directory; how to redirect old URLs

[Khalid]

A few years ago I started a website with WP installed in a subdirectory (let’s call it ‘/folder’) to keep the root clean. Now I want to apply the following tutorial: Giving WordPress Its Own Directory – Using a pre-existing subdirectory install. It’s easy to apply but I don’t want to lose my Google ranking. So how can I redirect the URLs with ‘/folder’ automatically to the root?
For example: mydomain.com/folder/post-1 should redirect to the new URL mydomain.com/post-1, mydomain.com/folder/post-2 should redirect to the new URL mydomain.com/post-2 et cetera.

I guess I can fix it in the .htaccess file with 301 redirects, but after some research I still haven’t found a working solution.

[Khalid]

I’ve found this article on Perishable Press, with the following solution:
RedirectMatch 301 ^/blog/$ http://domain.tld/

It works for posts and pages, but not for the archive pages of categories, authors, and tags.

[Author]

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