404 error /wp-admin/admin-post.php when saving

Hello,

i’m facing some 404 issues with RankMath. When i try to save in the general settings and 404 monitor, i end up with a 404 error on website/wp-admin/admin-post.php

I have another weird issue. If i put a custom robots.txt in my ftp and check it on my website, it always shows a default robots.txt file. I can’t even use the robots.txt editor in rankmath (404…).

I desactivated my plugins, reinstalled wordpress, reinstalled the plugin, already contacted my host and they told me there’s nothing wrong on their end.

I’m really lost and don’t know what to do. Btw i know that “Search engines discouraged” is checked. I want to fix my robots.txt before unchecking it.
Could you help me please (and check if the 404 errors looks normal in the 404 monitor aswell) ? Thanks!