A busy scene becomes slightly softer, then sharpens again when you turn toward a quieter area. If dynamic resolution is enabled, the game may be changing the size of the image it renders internally while the monitor continues to display the same output resolution.
Unity’s documentation describes dynamic resolution as a way to reduce rendering work for the GPU by lowering resolution when needed. The feature’s availability and behaviour depend on the game, rendering pipeline and platform. It is not a guarantee that every demanding scene will reach the target frame rate.
Separate three numbers
The display’s resolution describes the output you see. The internal render resolution describes the image the game initially draws. The frame-rate target describes how often the game is trying to deliver frames. Dynamic resolution changes the second in an attempt to help with the third, while the first can remain fixed.
As a simple illustration, rendering each dimension at 75% produces about 56% of the original pixel count, because both width and height change. That does not translate into an identical percentage improvement in performance: other work still has to happen, and the game may be limited by something besides pixel rendering.
Compare a repeatable scene
Use the same route, camera position and graphics settings when comparing the feature on and off. Look at fine geometry, distant foliage and moving edges, as well as the frame-time behaviour. A still screenshot can miss changes that become distracting during movement.
Also check whether the game combines dynamic resolution with an upscaling or reconstruction method. A fixed render scale and a dynamically changing scale are not the same setting, even if both can make the internal image smaller than the final output.
Choose the result you prefer for that game: steadier motion may matter more in one title, while stable fine detail may matter more in another. Record the setting with the game’s version and platform. That makes the comparison reproducible instead of turning one scene into a claim about all games.