But you mentioned the colour correction is set to grey scale, isn’t that exactly what you want from reading mode? It’s also possible to set your display to grey scale in the settings for “modes” so you could create your own mode there called reading mode and change the display settings for that custom mode.
Just tested this, the colour correction only affects the displayed image on my device, not screenshots
Not sure when the ability to add custom mode was added (I’m on android 16), but it’s part of the menu that contains bedtime mode, driving mode and DND (edit: custom modes were added in one of the android 15 updates). You could use one of those preset modes and set the display setting for it to grey scale, but I’ve noticed that colour correction actually has a quick settings toggle, so you could use that with colour correction set to grey scale as a sort of reading mode as well. Here’s what my modes menu looks like on my phone:
