On an Android phone you can use firefox, ublock origin and youtube in the browser, too. It also supports playing in a floating window (fullscreen the video and then switch app from firefox to something else).

I noticed this is starting to be less effective. Now and then an ad creeps through the protection barrier. First time it happened to me was exactly at the moment I was demonstrating someone that I really do have an ad-free internet experience :/

i'm using vanced and it works really great, the only ads that i rarely see are the "recommended promoted video"

There's also Youtube Vanced.

It has an adblocker but also SponsorBlock, which is amazing. It skips all the annoying tedium of YouTube videos (intro, self promotion, sponsors, credits)

I couldn't go back to Youtube without adblock and SponsorBlock.

It also has this amazing "skip silences" feature.

You can do background play in Safari iOS by switching to desktop mode, press play, lock the phone and then click again to play from lock screen / outside safari. Alternatively friendly does also background play.

This is tangentially related, but Google has been blocking iOS native PiP mode on YouTube on iPhones on the website.

Here's a bookmarklet (you must create and edit an existing bookmark with the contents below, else you will get an error) that will pop out a YouTube video on iOS into a PiP video when run. Simply click on the Bookmarks while on the YouTube page and select it.

This allows you to play the videos in the background by swiping the PiP player off to the side.

Disclaimer I do not remember where I got it, only that it seems to work for me.

javascript:(function()%7Blet%20v%20%3D%20document.querySelector('video')%3Bv.addEventListener('webkitpresentationmodechanged'%2C%20(e)%3D%3Ee.stopPropagation()%2C%20true)%3BsetTimeout(()%3D%3Ev.webkitSetPresentationMode('picture-in-picture')%2C%203000)%3Bcompletion()%7D)()

How does Google manage to block iOS PiP and why doesn’t Apple write some workaround in its Safari engine?

Vanced is also really good. Supports YT Music too.

Is there any App that can do the same on Smart TV? Getting tired of ads on Youtube's ads.

As per the Sponsorblock extensions Github page only App for Android based Smart TVs with sponsorblock buitin appears to be Smart Tube Next [0]

[0] : https://github.com/yuliskov/SmartTubeNext/

I use https://github.com/yuliskov/SmartYouTubeTV

It ah the same UI as youtube, but no ads.

just a heads up:

They have their own repository [0] which has faster updates.

[0]: https://newpipe.net/FAQ/tutorials/install-add-fdroid-repo/