https://www.majorgeeks.com/content/page/youtube_double_tap.h...
YT also has Premium Controls whcih is a widget but I think it's experimental and not on mobile yet.
1. There is enough room. Works fine for media controls where the bar is near the bottom of the screen, but not for sliders in most other places
2. The control is not close enough to the bottom of the screen for swipe up to trigger the multitasking action
There are many other reasons to have fine-grain control for sliders and imo “hold longer for finer control” works in more places than “slide up for finer control”
It's not really "slide up" its just a very tiny motion, maybe less than 1cm of travel to enable it.
We already have long press and 3D Touch events via the "hold longer" action, which might work, but I've had no real issues with the YT solution.
When your slider is not controlling video playback
YT implementation turns the fine-tuning seekbar into a series of thumbnails to help find where you are.
Stuff like this obviously doesn't make sense for controlling something that is not a video.
I do like some tools which let you fine-control slider once you have click-and-held by scrolling the mouse wheel, but no solution here for mobile.
This works in my modded old version of the YouTube app; Alphabet might have removed it in newer versions.