Hi. I have the same problem. It started a few weeks ago. Can’t edit any pages, create any new pages, or view or edit the media. Only thing I can do is configure wp. Also can’t edit the theme, view or customise it.
Steps I have tried:
1. Delete all plugins
2. Reinstall all plugins
3. Upgrade all plugins
4. Disable all plugins
5. The same as the above 4 steps but themes.
6. Entirely delete wordpress and its database and start over from scratch
7. Edit the .htaccess file and add
<IfModule mod_substitute.c>
SubstituteMaxLineLength 10M
</IfModule>
8. Chmod -R 777 *
9. Chown -R www-data:www-data *
10. Step back the PHP files to version 5.4
11. Step back the database to that that I had in Jan 2022.
12. Recreate the site entirely.
13. I have not changed any security config on the server or disabled XMLRPC.
It is doing this on many sites on the same server.
It is recent.
If I watch the system logs, I see it repeatedly try access the edit page. It tries roughly once a minute and then retries five times before returning a white error page showing that there was a zero response frm the server.
I do not have woocommerce.
I do not have jetpack.
I have tried the obvious things like deleting special block editors, or the gutenberg one, or re-enabling it.
The PHP is 7.4 and it allows up to 8gb uploads and 8gb RAM usage, and 1000 file uploads. I set it high so as to eliminate that as a possible cause.
It DOES let me do a quickedit to set the owner, date, time, etc., of each post-page, but nothing else.
I am at my wits’ end.
—-
OK so an update: restarting apache helped. Very peculiar.