WordPress wplogin is not aviailable after copying installation into subfolder

First: I know that this question is existing in many variations and that there have been many answers but none of the solutions worked for me.

I have a working instance of WP running on my server, but I want to work on a new design and parallel run the old site.

1. So I created a new subfolder called “neu” on my server and copied all WP-Files I in this folder.
2. I Also created a new database and imported my old database-file via sql inside the new database. I changed the data in the wp-config file and added

define(‘WP_HOME’,’example.com’);
define(‘WP_SITEURL’,’example.com’);
define(‘RELOCATE’, true);

to my wp-config.

3. I adjusted my .htacess and changed the entrys to

RewriteBase /neu/
RewriteRule . /neu/index.php [L]

4.I went to my database with PhpMyAdmin and changed the 2 entries in the options table to https://www.myurl.de/neu

When I go to the new site i can open the front end sites, but when I try to go to the login page I get a 404. So I am not sure what else could be the problem here… I realy hope that someone can help me!

the site is: https://www.nrc-makler.de or https://www.nrc-makler.de/neu