Nginx rewrite gives 404 - nginx

Question

On a server with Ubuntu 20.04 and nginx 1.18.0 using ISPConfig 3.2 I have the following configuration for my Wordpress website:
location /api {
rewrite ^(.*)$ $1.php last;
}
location ~* ^/index\.php$ {
break;
}
try_files $uri $uri/ /index.php$is_args$args;
location /user {
try_files $uri $uri/ /index.php$is_args$args;
rewrite ^/user/([^/]+)/([^/]+)/master?$ /index.php/master/?userid=$2 redirect;
rewrite ^/user/([^/]+)/([^/]+)/chief?$ /index.php/chief/?userid=$2 redirect;
rewrite ^/user/([^/]+)/([^/]+)?$ /user/?userid=$2 redirect;
}
The redirect for e.g. /user/john/123 to /user/?userid=123 is working as expected.
But I do not want a redirect but to keep the URL as it is and show the content of the internally rewritten URL. So I tried to change redirect to break or last but both changes are resulting in a 404.
...
location /user {
try_files $uri $uri/ /index.php$is_args$args;
rewrite ^/user/([^/]+)/([^/]+)/master?$ /index.php/master/?userid=$2 last;
rewrite ^/user/([^/]+)/([^/]+)/chief?$ /index.php/chief/?userid=$2 last;
rewrite ^/user/([^/]+)/([^/]+)?$ /user/?userid=$2 last;
}
Why is it working with the redirect but not without?
Edit
Another try:
location /api {
rewrite ^(.*)$ $1.php last;
}
location ~* ^/index\.php$ {
break;
}
try_files $uri $uri/ /index.php$is_args$args;
location /user {
try_files $uri $uri/ #userrules;
}
location #userrules {
rewrite ^/user/([^/]+)/([^/]+)/master?$ /index.php/master/?userid=$2 redirect;
rewrite ^/user/([^/]+)/([^/]+)/chief?$ /index.php/chief/?userid=$2 redirect;
rewrite ^/user/([^/]+)/([^/]+)?$ /index.php/user/?userid=$2 redirect;
rewrite ^/(.*)$ /index.php?$args last;
}
Same result - if I remove the redirect it results in a 404.
The resulting page e.g. /user/?userid=203 works but I would like to keep the readable URLs.