YouTube Vanced was one of the very popular modded versions of YouTube that offered high-end features like ad-free videos, background video playback, and AMOLED dark theme. Even though it is officially closed, you are still able to download and install it through third-party sources. To achieve this, first of all, look for "Vanced Manager APK" on a trusted website. Download and install the APK file, then launch the Vanced Manager application. From there, download MicroG (necessary to log into your Google account) and then download YouTube Vanced. Be aware that because it's no longer supported officially, there are security concerns, so only download from reputable sites. Alternatively, you might try YouTube ReVanced, an updated alternative with similar features.