Solution:
This error is due to the absence of permission given to the wordpress files. All the folder permissions should be 755.
chmod -R 755 /for all folders
And all the file permissions should be 644.
chmod -R 644 /all the files
You can also check the wordpress GUI and check the site health(Tools > site health)if your health status is not good, scroll down and see the errors over there,needed permission for each file will be mentioned over there and give the permissions accordingly.
Only for try
chmod -R 777 /parent folder where all the files are included if this works you can confirm that your issue is with the permission.If that didnt work check out the memory and the wp-config.php file