If you see the "unable to capture a screenshot, all possible methods failed" error when using GNOME Screenshot in Ubuntu, it is not a bug – but by design.
You're reading Why the (Old) GNOME Screenshot App Doesn’t Work in GNOME 49, a blog post from OMG! Ubuntu. Do not reproduce elsewhere without permission.
The GNOME 42 alpha release is available to download with many major changes, ranging from GTK4 ports of core apps like Nautilus to a bold new look.