For non FOSS i use Niagara, for FOSS i use Kvaesitso

Navigate to the Releases tab. You'll find every app versions released by the dev. In the bottom of each version there is a Download section, click the file with .apk and install it manually on your phone

if you're talking about alternative ui/ux, you could try Piped/Invidious instances. Usually I use piped.kavin.rocks or yewtu.be to visit youtube on desktop browser. It basically youtube without ads and other bloats, also privacy-friendly. Or as other stated, you could try NewPipe or Libretube on smartphone. Keep in mind that all of these alternatives wont provide you google login functionality. These apps only store your search history locally on your device. It takes a bit of time to get used to not get fed by recommendation algorithm and not doing any mindless scrolling

The price to pay for convenience is too steep for most people to migrate. Also if you just an average user, most of the time you will not get instant gratification for being more privacy-aware. The more you try to be more aware the more you realize that to achieve a certain level of privacy is really a pain in the ass.