How can I get finer resolution steps on a virtual screen?

Use the virtual screen's generated resolution list and reduce its Resolution step multiplier. BetterDisplay generates its sizes from the virtual screen’s aspect ratio, so you do not need to enable flexible scaling as you would on a physical display.

For the underlying rendering method, see what flexible scaling and custom resolutions change.

Open Settings > Displays > [virtual screen]. Leave Use custom resolution list off to use automatic generation, then open Additional Resolution Settings… and lower Resolution step multiplier. This setting requires Pro. Select Reconnect when prompted to rebuild the modes. Save your work first, because reconnecting temporarily removes that virtual desktop.

The aspect-ratio numbers also affect spacing. A ratio expressed with large, irreducible numbers can leave widely separated sizes even at the smallest multiplier. A nearby simpler ratio can provide more intermediate choices, but it changes the shape slightly and may leave unused pixels when presented on the physical screen. Use the actual target dimensions to choose a ratio rather than copying one from another device.

Check Limit resolution range if the list is unexpectedly short. A narrow range restricts the generated choices. Very dense combinations of resolutions, refresh rates and SDR/HDR variants can also be reduced to fit the mode budget, so the smallest multiplier does not guarantee every intermediate size.

For an iPad connected through Sidecar, configure the BetterDisplay virtual screen and then mirror or stream it to the Sidecar display. The virtual screen supplies the desktop sizes, while Sidecar carries the image to the iPad. Changing resolution can change text size, but this does not automatically keep text at the same physical size across all your displays.

To set this up for Sidecar using the Pro matching and mirroring features:

  1. Connect the iPad, then open Settings > Displays > Overview > Create New Virtual Screen….
  2. Choose Match aspect ratio of and associate to a display, select the Sidecar display, and keep association enabled.
  3. Turn off Configure full screen stream to this display and enable Configure virtual screen mirroring.
  4. Create the virtual screen, then choose a desktop size in its Display Mode menu.

Streaming is an alternative when you need rotation or other presentation features. See portrait Sidecar setup. Creating a virtual source does not raise Sidecar’s own transport frame-rate limit.

See Virtual Screen resolution settings and mirroring, streaming and PIP.