I finally managed to resolve the issue: I have re-installed the latest version. Hope it can help someone else!

The error has appeared from one day to the next without me making any changes so I don’t understand why it shows an error about memory size. I have not changed anything at my site since early October.

For me, it was related to a plugin, try this:

As you are unable to access your WordPress admin area so please try to access your file manager in cPanel or access public_html directory via FTP.

Go to wp-content/ Directory them rename plugins/ directory to pluginsbackup/ now try to load your site. If this works that means you have problem with a plugin.

If problem is with plugin change back the directory name pluginsbackup/ to plugins/ Enter in plugin directory. Now rename each plugins directory by placing backup at end of that directory name.

Once you have changed all plugins directories names, start getting original directory names one by one and make sure you check the website if that’s still working after each plugin start working. As soon as you see which plugin is making problem just delete that plugin.