The checkbox with the text “Don’t show this again at start up” of the Welcome window in dark themes (like Breeze Dark in KDE and Yaru Dark in Ubuntu 20.04) is still unreadable when it has no mouse focus. The text appears when the mouse passes over the checkbox.
It is readable when the theme of the operatiion system is light (like the Yaru Light in Ubuntu).
I usually sit these out, but I have little to no use for Dark Themes. I know they look elegant and all, but they actively interfere with human sleep cycle display color and brightness changes.
You can turn all that dim and orange business off, but then you get stuck with the blue screen optical bio-triggers and more sleep problems.
“No, it’s not daytime. It’s midnight and I really need to get to sleep.”
So yes, that in addition to text vanishing under certain theme applications and conditions.