Hello,
1/ Enable debug mode in WordPress – https://wordpress.org/support/article/debugging-in-wordpress/ to find out what error appears on your site, it will point you in the right direction what needs to be fixed.
2/ Please record a video for us of your actions.
3/ Provide temporary wp-admin access.
wp-admin access: Create an account via Dashboard (Users > Add new) with administrator role http://prntscr.com/s3rc9m > provide us with username and password via the Private Content area http://prntscr.com/s5mao7 You can use any email for it.
Regards