Does this issue happen on other libraries? Or other lists? Create a new library and check the results.
Does this issue occur with other site collection admins? Please add a new user and then set the user as site collection admin to see what happens.
I guess you are working on a Office 365 Group Site, which has several differences from the type of SharePoint site. You can try to install SharePoint Online Management Shell, PowerShell, and follow this post to enable the custom scripts for SharePoint Online Group Sites.
After doing above steps, go to library settings and check the results.
Note: There are different kinds of admin roles in SharePoint Online, for more information about SharePoint Online admin role, you can read this article.