Hi Алексей,
I can confirm that I'm logging in as a separate user as opposed to using the "Switch role to..." feature. For example, when I first go to my site, I am not logged in as any user (navigation bar just shows the words "Log in"). However, as soon as I click on a page (we have a number of links available to non-logged-in users), I am automatically logged in as "Guest" (at which point the navigation bar shows the word "Guest"). Of course, at any point I can click "Log out" and then use the actual login block to login as an official user.
I went to the Navigation block > Assign roles > Permissions and added "Advanced role overrides" for the three roles I mentioned (Front Page User, Guest, and Authenticated user) so that the "View block" (moodle/block:view) permission is now set to "Prevent" instead of "Prohibit". I also tried purging caches and using different browsers, just in case there was some kind of cache issue, but I'm still seeing no change and the Navigation block is still showing up for all users.
Any other suggestions?