My monitor used to offer 4K but now only offers 1080p. Do I need BetterDisplay Pro?

Start by restoring the display mode that previously worked in macOS. A sudden loss of an available 4K connection can come from the monitor’s settings, cable, adapter or how the devices establish the connection. Check those first before deciding whether you need Pro.

Check whether the missing value is the actual connection resolution or the desktop’s HiDPI “looks like” size. A desktop that looks like 1920 × 1080 can still use a 3840 × 2160 image. BetterDisplay’s Display Information helps you inspect what is connected.

The macOS scaling explanation distinguishes desktop size, rendering pixels and physical output.

Check the monitor and connection

• Review monitor settings changed recently, especially gaming modes that trade resolution for a higher refresh rate. A frame-rate boost mode can restrict the monitor to a lower resolution. Check the monitor’s manual before changing them, because their effects depend on the model.
• Power-cycle the Mac and monitor, then test a different suitable cable or port. If a dock, hub or adapter is involved, test a direct connection where possible.
• Check the resolution and refresh-rate support of the entire connection. Apple explains that an unsuitable cable or adapter can produce a lower resolution or refresh rate in its external-display troubleshooting instructions.
• If necessary, record the monitor’s settings before a factory reset, and compare its behavior with another computer.

If macOS again offers the expected connection resolution but you want a different interface size, investigate scaling separately. A missing scaling option and a connection limited to 1080p are different problems.