Just works, for now at least.
takes a few tries and maybe a page reload to get going, also the default of 100 never works. you need to set it at 1000 or some other large number and just refresh the page when it quits working and when you wanna stop the process.

Time saver after a few stops did continue after restarting. Did get them all eventually.

Doesn't work

It doesn't work

It does the job for the most part, with a lot of trial and error I was able to whittle down a list of 4000. It does not know how to handle unavailable videos however.
Clicking the default value never works, and it never consistently reaches the value you give it.

Only one that worked after around 6 years of searching for something like this every other year or so. Sometimes YouTube needs a rest for a few hours before you can do it again, but finally clared my 4500 video watch later playlist in a few hours. Great work!

Doesn't work.

deleted my 2k video playlist in about 10mins :)

Not useful in its current functionality. Would be more useful to be able to delete top of list or something.

It works, I just removed 600 unwatched videos. Go to https://www.youtube.com/playlist?list=WL and start the plugin. Try it multiple times, sometimes is throws an error.

Does not work: https://github.com/franleplant/youtube-watch-later-mass-delete/issues/1