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You probably have a problem-causing plugin.

Look at the error.log file which will tell you the file that is causing the problem. Rename that plugin’s folder (use your hosting control panel’s File Manager) and retry. That should get you into the admin area. Then you can contact the plugin’s support forum to figure out the fix – or just delete the plugin.

Alternately, you can rename the entire plugin folder (in wp-content) so that all plugins are disabled, then move those plugin files individually by their folders to re-enable them.

But looking at the error.log file (via your hosting cPanel or via FTP program or hosting File Manager) will help you zero in on the problem.