If Flameshot's screenshot selector on Linux keeps popping up on the wrong monitor — even one that's turned off — check your primary display setting before anything else.
On my Gentoo + XFCE4 + X11 setup, Flameshot (Flatpak) kept opening its capture overlay on my second monitor, no matter what I did. Compositor tweaks, permissions, config resets — nothing worked.
The actual cause: my main monitor wasn't set as primary in XFCE's display settings. Flameshot just follows whatever XRandR reports as primary, regardless of which screen is actually active.
One change in Settings → Display, and it's been working perfectly since.
