Ancient needs a supported overlay running before you inject.
NVIDIA GPU
NVIDIA cards can use the NVIDIA App overlay or SteelSeries. GeForce Experience does not support fullscreen in-game.
Install the NVIDIA App.
Open Settings → General and enable IN-GAME OVERLAY.
Full steps: NVIDIA Overlay Setup.
AMD GPU
AMD cards support SteelSeries only.
Install SteelSeries GG.
Open Settings → GENERAL → General and enable Sonar.
Open SONAR → Shortcuts and assign
F7to Master - Volume Up.Press this key before you inject.
Full steps: SteelSeries Sonar Overlay Setup.
Important
Set Rust to Borderless Fullscreen, not Fullscreen Exclusive. Fullscreen Exclusive can crash the game while the menu initializes.
Synthera Docs