It could also be caused by a plugin. Check your wordpress plugins. To check for a plugin conflict you can temporarily deactivate all other plugins, and then see if it Screenshot by Lightshot this works like try to update wordpress core.
First disable all security modules - CSF, modsecurity etc
Secondly disable all plugins
Test if you can update WordPress core
Activate plugins one by one testing editing a post or page/ updating core/ leveraging WP-REST API etc
Till I know, the firewall is the one conflicting because this is happening in all WordPress accounts and they have been built for 2 3 years running on other servers and now on cyberpanel so it’s not about plugins
Can you share with me the best settings for cyberpanel firewall CSF/ModSecurity etc
Personally I do not use CyberPanel ModSecurity because development stopped long time ago. And i do not recommend it for any of my customers. Prefer CloudFlare WAF, Imunify
As for CSF its just a packet inspection app that from experience only stops intrusions such as bruteforce exploitations such as wordpress XMLRPC. The default configuration is sufficient enough. Install as is and csf will do the rest. Prefer CrowdSec
Thanks bro, I was experiencing the same problem, all my wordpress websites were slow and in the Query Monitor it was showing cURL error 28, after I changed the the DNS resolver it was back to normal. So much thanks!