Yeah, it's a Tauri app, which makes the claim in the README about it being a native app also rather a lie.
Did Tauri ever figure out how to run performantly on Linux, or are they still using webkit2gtk? They were looking at integrating Servo last time I checked, but I have no clue how far they've progressed with that since.
It's still webkit2gtk. A chromium version is in the works but it seems to use x11 under the hood..? So still not great.