Thanks for reaching out in the Community today with your question!
I did a little experimenting in my own store using the Simple Theme to track down where the information for 'Log in' and 'Sign up' are housed. It looks like these options are only visible in your header when you have customer accounts set to 'required' in your store. When using the 'Simple' theme without required customer accounts, no options appear in the header.
The menu item called 'Community' belongs to one of the menus you've built in your Navigation settings in your Admin. You won't be able to get that menu item to appear with 'Log in' and 'Sign up' unless you make a coding change to your theme that moves that menu item from that specific place to somewhere different.
Shopify employees working in Community Support don't have the expertise to advise on coding changes within your theme, but you can likely reach out to our live support team and find some assistance. Since you're using a Shopify developed theme, our team likely get you in contact with our Theme Specialists and they may be able to help you make this desired change. You can contact our live teams through this link here: https://bit.ly/3c5icUc
Another option you have is to reach out to a Shopify Expert and see if they can provide you with some assistance. Shopify experts are external partners that specialize in helping folks ramp up their Shopify businesses. You can access Experts from the Expert page found at this link.
Hopefully you find this information to be helpful! Please let me know if you have any questions.
Imogen | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog