Just tried again. I can see a slide but it doesn't seem to want to move when I either swipe the line or the icons. S22+. UPDATE: I can only seem to access it by going to landscape view
The spoiler and help buttons don't move, you need to slide the bar from anywhere to the left of them.
@Duluth Murphy's Law I tried again just this now with a total of 997 characters on a talk thread that previously rejected it and hey presto it went through. Thanks for your help, hopefully the initial problem has gone away!