Android 7.1.1 and 7.1.2 (Nougat) reached their official End of Life (EOL) several years ago. Google and YouTube have dropped support for older Android versions in their latest app updates. This creates a specific set of challenges regarding security and app functionality.
If you want the absolute latest features (like Super Thanks, newest UI changes) but can't install the app, use the browser.
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You cannot use the latest version. You need a version released roughly between late 2017 and early 2019.