I can't say I'm surprised given how popular it's gotten, but it's sad to see it go. Not just because of the abysmally shameless amount of ads they force on you so you'll buy premium, but also because of SponsorBlock.
On iOS, I've never gotten round to going down the route of "Sideloading" apps to get a cleaned up YT. I either use a non-Safari browser to force desktop mode so I can play with the screen off, or I use the main app and get sick of ads and close the app rather than sit through the same jingles and voices.
Even if people keep it going with updates, it will be a bit more sketchy now if it isn't from an established and trusted source.