Other people have complained on this and other ubi games of aim assist turning itself off. I have the opposite problem, on PC: I want to play in Aesir, but aim assist randomly turns back on.
This may be tied to Valhalla saying I have a controller during startup. I have never had a controller connected since I installed the game. Bluetooth has never even been on in that time. There is no controller in device manager. Regardless, the game knows I am playing with mouse even if it thinks there is a controller present, so this behavior is unacceptable even if a controller were connected. I start the game windowed because it takes millennia to check add-ons, then I go fullscreen with Alt-Enter.
Mouse is a Glorious O-, kb is an XD75, if either matters. There's also an external HDD with an SD card slot. No other peripherals.