Creating an account on chromium on Android and the yellow create account button disappeared as I scrolled down to press it. It reappeared when i rotated screen around to landscape mode.
My text & display sizes are set bigger than default in Android settings
My browser also has chrome://flags/#enable-tab-groups enabled by default which was covering the bottom of the screen (I had bonfire open as a tab in a group) and may be playing into this a bit? Initially I could see the yellow button. Later could see just the very top sticking out from behind the tab group bar, later it vanished. Just saw similar with the edit profile screen and the yellow button at the bottom of that
