Peter Massey-Plantinga

A conditional two-level menu only shows the second level of the menu on relevant pages.
For example, if you had a menu that had a structure like so:
<ul>
<li>Home</li>
<li>About
<ul>
<li>History</li>
<li>People</li>
</ul>
</li>
<li>Contact
<ul>
<li>Mail</li>
<li>Phone</li>
<li>Email</li>
</ul>
</li>
</ul>
You would only be able to see the “History” and “People” menu items on the “About,” “History,” and “People” pages.

Two Level Conditional Menu

This plugin converts a two-level menu to a conditional two-level menu.

Jonny Harris

Use classic menus in gutenberg, using this block. This block renders classic menu data using wp_nav_menu function, improving backwards compatiblity.

Two Level Conditional Menu vs Classic Menu Block