Google’s Terms of Service explicitly forbid modifying their app. While Google rarely bans for sideloading (they can’t detect the IPA on your phone easily), they detect anomalous API calls. If your patched app tries to fake a getPremiumStatus request 1,000 times, your Google account might receive a temporary restriction. Use a secondary YouTube account.
Since build 11499, the patching community has struggled. YouTube versions 19.x and 20.x introduced: youtube 11499 ipa patched
Modified YouTube applications offer several enhancements that go beyond the basic video-watching experience: youtube 11499 ipa patched