Hello @tomwphoto,
If you cannot access wp-admin, there are other ways to deactivate plugins: https://www.ads-software.com/support/article/faq-troubleshooting/.
Summary: you can using FTP and rename the current theme from root of the website / wp-content / theme / {{current theme name}} and deactivating any plugins with rename plugin folder(e.g, add -t) from root of the website / wp-content / plugins {{Plugin Name}}
To see the error on WordPress, you can check the super administrator email; Or turn on the WordPress debugger mode. To enable it, please follow the steps explained in this link: https://www.ads-software.com/support/article/debugging-in-wordpress/.
Then please share the error message here as a code.
We’ll find out what happened on your website with that error message(debug log).
After fixing the error, please tell us a little about the versions of plugins you use. To do this, please go to WP Dashboard > Tools > Site Health > Info Tab and click on the button Copy site info to clipboard.
You can send the information as code here or upload them to https://pastebin.com/ and get an exclusive link.
Note 1: you can ask your host provider to return the backup.
Note 2: If you have any cache plugin or server cache(CDN / Browser Cache and Cookies and …), you need to clear its cache contents or disable them to see your changes. Also, don’t forget to click on the regenerate all assets file and data in Elementor > Tools.
Please keep us posted.
Best Regards