Is this about Gnome’s on-screen keyboard not working properly in Chromium Flatpak or does Chromium bundle its own on-screen keyboard?
I see you’ve already replied in also created #19937.
I’m going to assume this is about Gnome’s on-screen keyboard below.
Can you be a bit more specific about your issue?
Does Gnome’s kb pop up and fail to register any key presses or does it simply not come up altogether?
Does it work as expected in other apps?
To enable the kb in Gnome: Settings > Accessibility > Screen Keyboard
Are you using Wayland and if so does Chromium launch with the Wayland backend or run under XWayland?