Hi,
Thanks for reaching out.
To add a new “Blog” menu item in the header Menu follow these steps:
1. From your WordPress Dashboard, go to Appearance > Editor.
2. In the left sidebar, click on Navigation:
3. You’ll see your existing navigation menus. You will see “Header Navigation” click the three dots (⋮) next to it, and select Edit.
4. The navigation editor will open. Click on the + (plus icon) to add a new item.
5. Select your Blog page from the list or add a custom link if needed (e.g., /blog).
6. Once done, click Save at the top right.
You can also check this detailed guide on the Navigation Block: https://wordpress.com/support/wordpress-editor/blocks/navigation-block/