Flatty
If I check all required permissions of Line there, it shows over 60 detailed described permissions
The site you're referring to has highly inaccurate and misleading info about permissions. We explained why above. You should stop using the inaccurate info there and use the proper built-in permission management system.
+3 trackers
This is inaccurate too. The site can't actually detect whether apps are privacy invasive. It detects a specific list of third party libraries they deemed trackers. It can't detect anything not on that specific list. A lot of their list is also quite misleading as is how they're branding it trackers. It's simply not a good way to understand privacy.
after installation on device and granting no permissions in app settings (which only 11 permissions settings are visible and allowed to be toggled) to it, it will be harmless towards the data on my phone anyway, since no any of mentioned above over 60 required permissions will be given to the app. Do I understand correctly?
No, it's not correct info in the first place. Use the interfaces built into the OS. You can view the full set of requested permissions in the OS. You can see that the standard permissions are categories with a bunch of sub-permissions and that they enable/disable those. All standard permissions are off by default. Sensors and Network are special since we add them and they aren't usually there, so Sensors is on by default but there's a toggle to set it off by default for newly installed apps along with it having a notification when apps are denied access since they don't know how to check for it or request it. Network is handled at install time since apps know how to request it at install time but not runtime.
The other category is handled via special access permission toggles and case-by-case requests such as power optimization exceptions or Bluetooth pairing. Many are simply not relevant to privacy. You need to look through that and ask about something specific that you're concerned about. Exodus is inaccurate info and not worth bothering with.
And how about the trackers? How GOS handle them? Or external app is necessary to manage trackers traffic?
The site you're using (Exodus) has inaccurate information about this. There is also nothing specific to manage. It's already handled by the standard app sandbox and permission model.
To understanding this, would help me to decide where should I install this app on my phone. If it would appear to be safe for my data, after all permission denying, then I would install it at my User account where most of my trusted apps are located and I store sensitive data. However, if despite of giving no permissions this app will still try to harvest my data somehow, then I would prefer to install it in another User profile, where I keep only untrusted/privacy invading apps.
Apps are sandboxed regardless of the profile you install them. The profile is not the app sandbox. Apps can see the other apps in the same profile and if both apps agree to it they can communicate.