Navigation inheritance not working for communication site to subsites

Michael Henriksson Microsoft recommends using flat site structure in SharePoint online instead of sub sites.

You can have same theme and navigation for multiple sites using hub site and associated sites concepts.

Check below Microsoft official documentations for detailed information about this: 

1. SharePoint information architecture - Guiding principle: the world is flat 
2. Planning your SharePoint hub sites  

Please click Mark as Best Response & Like if my post helped you to solve your issue. This will help others to find the correct solution easily. It also closes the item. If the post was useful in other ways, please consider giving it Like.

For SharePoint/Power Platform blogs, visit: Ganesh Sanap Blogs