Can't Log Into WP Dashboard

When I try to log into the WordPress dashboard, I get an error message:

“Sorry, we can’t find the content you’re looking for at this URL. Please try selecting a menu item from above or to the side of this message to get where you’d like to go.”

This is the URL: (the login page is here: )

I get the same error message when I try to go to any page inside the dashboard (e.g.

I’m able to log in, technically, but I get redirected to the error page and am therefore not able to access the dashboard.

I don’t know what is causing the problem, but the site is on Cloudflare and also integrated with through the Jetpack plugin.

I would appreciate it if you could give me some advice on how to fix this problem. Thanks.