I have a WordPress experience of 5 years on fixing and debugging as well like fix 500 internal server errors and other WordPress errors.
Here are Some Common issues that I worked on before with 100% result output.
500 Internal Server error
404 not found error on Post/pages
Memory exhausted error / Increase PHP Memory
Forgot username/password
Redirection / SSL redirection issues.
Error establishing a database connection
WP update issues
Permission issues
Locked out of WordPress admin
Blank homepage
Image upload issues
Wordpress dashboard missing functions
Login page refreshing and redirecting issue
Fix 404 NOT found errors
Fatal error
White screen of death
The site is experiencing technical difficulties
Common 500 internal server error:
Basically, 500 internal server error occurs when you have made any recent changes on the admin panel, hosting Cpanel or while playing with DNS servers.