You use File Manager located in hosting or FTP client such as FileZilla. Then go to the public_html () => directory and look for the .htaccess file and edit it. You add the following code to the end of the .htaccess file

php_value upload_max_filesize 128M
php_value post_max_size 128M
php_value max_execution_time 300
php_value max_input_time 300
php_value memory_limit 256M

Option 1: WordPress 500 Internal Server Error due to plugins or themes
In many cases. WordPress 500 Internal Server Error occurs when installing or updating plugins or themes. If you know what plugins or themes are causing WordPress errors. You fixed 50% of the error.
Option 2: WordPress 500 Internal Server Error for installing or updating the plugin
If your site is buggy after installation or update. You can fix this by disabling or removing the plugin. Depending on the situation. There are 2 ways to do this.
Disable plugins via WordPress Dashboard.
If your WordPress Dashboard is still accessible. Please follow the steps below:

Log in to your WordPress Dashboard.
Plugins> Installed Plugins from the left menu
Install plugins section in WordPress Dashboard
Disable plugin causing errors.
deactivate plugin to debug wordpress internal internal server error
Reload the page to see if the bug is fixed.
If not. Disable other plugins and repeat the process until all plugins are disabled. (or until the site runs again)
Once you’ve found the plugin that caused the error, try removing and reinstalling it. You can find the same plugin or contact the programmer of that plugin. Check out why it’s not compatible with your WordPress.
There are many situations that make dashboard inaccessible. In such a situation. You can cancel or delete the plugins. with File Manager located in hosting or FTP client such as FileZilla.

Navigate to the root of WordPress and go to the wp-content / plugins directory.
Identify the error plugin and rename that directory to disable it.
If your site is broken for installing or updating a new theme. You can handle this by changing your theme. Select any theme and click the Activate button to use it. Now, you will reload your site in the browser and it will reload the theme. This method will fix this. You can try reinstalling your old theme. or contact the theme provider for more information on how to implement it.
Possibly due to lack of memory because PHP values are not enough. It may also be the cause of the error. WordPress 500 internal server error. Because scripts and plugins may require more memory to operate efficiently. Also, when your site loads. The browser also increases the number of requests to load plugins, scripts, and content. When the memory capacity is not enough for the plugin and the script to run. WordPress website will be able to extract 500 Internal Server Error. So to fix this you can increase the memory and other PHP values by editing the .htaccess file.
Here are the lines you should add:
php_value upload_max_filesize 128M
php_value post_max_size 128M
php_value max_execution_time 300
php_value max_input_time 300
php_value memory_limit 256M

Reason Can not save settings in theme panel. This is because I’m restricted to php in the .htaccess file.
I fix it by adding the following code:
php_value upload_max_filesize 128M
php_value post_max_size 128M
php_value max_execution_time 300
php_value max_input_time 300
php_value memory_limit 256M

I have successfully debugged, thank you very much!