I would suggest clearing your cache and trying to access the admin from your custom URL. This would look like yourstorename.myshopify.com/admin, Then enter the corresponding email address and password.
Check out these docs for some more details;
Thanks for reaching out in the Community forum. I appreciate you bringing your question here. I'm happy to help.
May I ask which browsers you've tried on? I noticed the screenshot you shared is Safari, have you also tried it on other browsers? It's important to keep in mind the Supported Browsers. If this continues, we'll need to access your account to take a closer look.
To speak with an advisor, visit our Help Center and log in to your account to create a support request. Once you have logged in, type your request in 'Ask about a topic', scroll down to 'Get Support' and then click 'Continue'.
Please let me know if there's anything else I can do to help in the meantime,
Just checking in! Are you still experiencing issues with store log-in? I want to ensure you receive all the support you may need.