Critical error ONLY IN BACKEND after migration

Hi there!
I logged today into my website and the system suggested an update. I’ve been updating all my other WP sites recently with no problem but in this case I clicked update and after some seconds it came back with a “cannot load page” error (I didn’t interrupt it)

After this, frontend would still load 100% ok but backend was “Critital error”

I disabled all plugins and this had no effect. Then I realized that the issue was only affecting backend so I disabled the admin/includes plugins (by renaming folder). This cause the backend to just show a blank page with no error but no content

Downloading errors.log gave this result:

[Sun Nov 13 11:26:06 2022] [warn] [client 95.39.231.28] mod_fcgid: stderr: PHP Fatal error:  Cannot redeclare use_block_editor_for_post_type() (previously declared in /var/www/vhosts/casinodelaunion.es/httpdocs/wp-includes/post.php:8105) in /var/www/vhosts/casinodelaunion.es/httpdocs/wp-admin/includes/post.php on line 2189
[Sun Nov 13 11:26:57 2022] [error] [client 104.247.72.136] client denied by server configuration: /var/www/vhosts/casinodelaunion.es/httpdocs/xmlrpc.php

So I renamed correctly “includes” folder but disabled admin/includes/post.php file. Again the backend would should a blank empty page.

What can I do to revert this?

Thanks!

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