websites not rendering correctly using Safari

Hi,

You disabled extensions but did you check plug-ins?

If not, troubleshooting help here > If Safari is slow, stops responding, quits unexpectedly, or has other issues - Apple Support

If that isn't the issue, third party fonts might be the culprit ..

Open the Font Boot app located in HD > Applications.

From the Font Book menu bar, click Font Book > Preferences then click Resolve duplicates by moving files to the Trash.

Quit and relaunch Safari to test.

If it turns out to not be a font issue, a Safe Mode boot deletes system caches that can help.

To start up in safe mode:

1. Start or restart your Mac, then immediately press and hold the Shift key. The white Apple logo appears on your display. If you don't see the Apple logo, learn what to do.
2. Release the shift key when you see the login window. If your startup disk is encrypted with FileVault, you might be asked to log in twice: once to unlock the startup disk, and again to log in to the Finder.

To leave safe mode, restart your Mac without pressing any keys during startup.

Then try Safari.

Use safe mode to isolate issues with your Mac - Apple Support

Try setting up another admin user account to see if the same problem continues. Also try the Safe Mode.

Isolating an issue by using another user account

If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

Etrecheck – System Information