For physics engine, yes. Unreal doesn’t support fixed timesteps by design (it’s intentionally done this way). You can force the rendering to tick at somewhat fixed timesteps and then do physics without substepping (that way physics would always tick only on rendered frames) but you wouldn’t be fully in control then either.
edit-> fixed framerate also only works if your target hw can render the game that fast, if it doesn’t it would change physics ticking rate too in that scenario.