The game silently defaults to using FXAA for antialiasing every time on startup, regardless of what setting the player has actually set for it. The player’s original, intended setting is still shown as selected in the graphics settings menu despite this. Changing the setting fixes this for the rest of the session.
Setting Antialiasing to None, then Temporal, then restarting the game.
The game to use Temporal AA when I started it back up again.
It changed back to FXAA, despite Temporal still being marked as selected in the graphics settings menu.
I just did a quick search before finishing this, turns out this issue has been around for at least 2 years now!