Sorry, there is confusion here in what we are asking for. This is not in relation to cpanel. This is your admin control panel on your community. We need admin access in order to look at the issue.
It sounds like everything hasnt been upgraded. Have you looked to check forums isnt showing disabled in System->Site Features->Applications? If its showing an incorrect version, please upload a fresh set of files from your client area, and run the upgrader again from /admin/upgrade
The only way you would be able to disable search completely would be to disable content discovery. However that would disable many search areas, including streams. You would do this by removing module permissions
You can disable search entirely by disabling the search module. Please see the guide below on how to do this
https://invisioncommunity.com/4guides/how-to-use-ips-community-suite/managing-members/member-permissions-r305/
We can provide only limits support for sites running on environments alternative to apache.
If you are getting an internal server error, you need to check your server error log to see what error you are hitting
Have you perhaps considered our cloud platform? I ask as if you are considering a change of hosting anyway, it would save you ever having this kind of situation again
Please see the response above from my colleague
https://invisioncommunity.com/forums/topic/464562-social-media-promotion-bug-facebook-parameters-out-of-date/?do=findComment&comment=2882896
Try increasing your memory_limit and then see if it runs. I suspect that is whats causing you the ossues, based on the above. There are other errors there, but those are not related to the invision software
Have you disabled all applications, plugins, and switched to a default theme? When you do this, do you receive the same error? Once we know this, we can then proceed