Why does choosing a HiDPI desktop reduce the available refresh rate?

A scaled HiDPI desktop can require more rendering work than the monitor’s native output dimensions suggest. The available refresh rates must fit both the display connection and the Mac’s rendering limits for that mode and display arrangement.

For the rendering background, see how macOS scaling, HiDPI and LoDPI work.

For example, a 3008 × 1692 HiDPI desktop normally renders at 6016 × 3384 before being scaled to a 3840 × 2160 monitor. It can therefore require a larger rendering surface than a 3840 × 2160 LoDPI desktop, even though the physical monitor remains 4K. See HiDPI and Resolution.

Compare complete modes in Display Mode: logical size, HiDPI/LoDPI and refresh rate all matter. Selecting the same width and height at a higher refresh rate may select a LoDPI variant. Check the resulting mode rather than assuming only refresh rate changed.

For an ordered comparison of desktop size, rate and HDR with a working return mode and restoration steps, follow Find a sharp HiDPI setup without sacrificing more refresh rate than necessary.

If adding another display or dock changes the available choices, compare the original direct connection and display arrangement. A monitor’s advertised maximum rate does not guarantee that rate with every scaled desktop and multi-display setup. Try a lower HiDPI size or another supported mode, and use Display Information to inspect the actual output and reported limits.

On some setups, selecting a working HiDPI mode at a lower rate first and then using App Menu > [display] > Refresh Rate exposes another possibility. Additional connection-level rates, when available, appear in a separate group with waveform icons. A rate offered there can sometimes work even when the ordinary mode list does not offer that combination.

This is not guaranteed: an unsupported combination can produce a black or incorrectly colored image. It also does not create a missing HiDPI resolution. Keep a known-working mode available, and only consider refresh-rate protection after confirming the result. Additional rates may otherwise be lost after a mode change. The Refresh Rate reference explains these choices and their persistence.

BetterDisplay can expose modes that are not obvious in the system’s basic menu, but it cannot guarantee a mode that the Mac and connection do not support. See HiDPI resolution limits.