Something is wrong. Your WordPress theme has got a blank screen and you can not log in to your admin through /wp-admin/ because there is blank screen too! At first, you may have check and disable all of your WordPress plugins, to control if the error is coming from plugins. After that, you can switch your WordPress theme directly from phpMyAdmin to check if the error coming from currently theme.
How to switch WordPress Theme in phpMyAdmin?
Step 1: Open your phpMyAdmin and log in.
Step 2: Find the right database.
Step 3: Find wp_options table (you may have another prefix, so look for prefix_options table).
Step 4: Find rows with value template and stylesheet, where are stored your active theme.
Step 5: Edit these two rows and enter there your new theme name. Name of the theme must be the same as your theme folder inside /wp-content/themes/. You can try any default theme like twentynineteen, twentytwenty or twentytwentyone.