Most probably one of the plugin is outdated and has caused this issue. I would recommend you to check error_log file to find the culprit plugin and update it to latest version. If it still causes issue, disable/delete it and report the issue to relevant plugin author.
Also ensure that you are theme is using the latest version.
Thank you kaushalsheth for your reply. I uninstalled all the plugins and tried to install wordfence first. I still got the error message. I updated 6 websites that are all built on themify themes and are all running the same plugins with a few different on each. Out of the 6 only 1 is having issues. What error_log files should I look in? I have looked in 3 so far with no current errors. Any help would be appreciated.
The new WordPress recommends a minimum of PHP version 7.3. Check php version of the website.
Also Errors like this are logged. Check the error log on your server. If you can’t find the log, please contact your host.
Meantime, enable wp_debug and wp_debug_log and after an error, look at wp-content/debug.log to see if anything gets logged there. https://wordpress.org/support/article/debugging-in-wordpress/
You can also try this: Please attempt to disable all plugins, and use one of the default (Twenty*) themes. If the problem goes away, enable them one by one to identify the source of your troubles.
For more detailed analysis,