hide elements of navigation bars in sharepoint site

the_common_starling 

The left most navigation (with My lists link) is called as a SharePoint app bar. Unfortunately, you cannot hide SharePoint app bar since March 31, 2023. There are some Microsoft unsupported ways to hide it but you should avoid doing it (check below link #2).

Check all related details at: 

1. Introducing a SharePoint app bar that features global navigation 
2. How to remove all sites bar and change the domain name in SharePoint modern site 

The second navigation is (Home, Documents, etc.) is called as a SharePoint site navigation. You can either move it top side below site title or completely hide it using SharePoint site navigation settings.

Check detailed steps for making site navigation horizontal or hiding it at: New Navigation features for SharePoint team sites 

Also, you can make the SharePoint site navigation links visible conditionally using audience targeting. Check this Microsoft official documentation for more information about this: Target navigation, news, files, links, and web parts to specific audiences 

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