wp-admin page error “This page isn’t working”

Greetings,

I was trying to upgrade my WP site to 5.8, not sure what happen and now i am not able to access my wp-admin page i am getting error “This page isn’t working” HTTP500

below steps i had try,
download the 5.8zip file.
take full backup of existing files/folders from server
replace all folders excluding wp-config.php.
the upgrade was not successful and site didn’t work
Then, i try to restore the old files,
delete all the files in the server and copy the files/folders from backup.
still the wp-admin and site didn’t work and getting the above error.

kindly assist.

Thanks & Regards,
Hasnain