Hildegarde

It’s because of the screen. Low frame rates are much less impactful on a small screen. When the screen takes up most of your field of view, you notice the frame rate more.

It’s not you, its the screen.

From context I get the impression that was a mistake and OP wrote Switch when they meant Deck. The rest of the paragraph seems to have pretty deck specific information.

You can see the edge of the screen at the titlebar on the right steamdeck, but not the left one. True black instead of dark grey.