Hi @Jasper_Wang ,
According to my research and test:
1, The "Department" is a template of Communication site, may I know what is the type of your site? Is it a Communication site? Please check.
For more details, there is an article for your reference.
2, About the "blog site", From July 17th, 2020, the ability to create new classic blog sites through the user interface had been turned off. So we’re afraid that there is no out of box way to create a blog site now in SharePoint Online.
To address your concern about the situation, we’d suggest you go to feedback on this issue, this is the best platform to let us hear from you and make our products and services better for you and others.
For a workaround, we’d suggest you create a blog with communication sites and news posts: you use news posts as your blog pages. Then, you can display those blog pages in a news web part filtered to show only blog pages. The latest blog pages will automatically display as the top-most news stories on your site (as you can see in the "Latest blogs from our executive team" news web part below). You can also link directly to blog posts from other web parts like the hero web part. To learn more about how to setup a great blogging site: Creating a blog with communications sites and news posts
Your understanding and patience will be highly appreciated.
Thanks,
Yanli Jiang
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