Preferences

Open File → Preferences… (Ctrl+,). Settings are saved and restored between sessions.

The dialog is organised into eight tabs:

General — startup and general options.
Media — the SD card slots and their read-only toggles (Next).
Display — scaling, aspect ratio and scanline defaults.
Input — keyboard and the classic joystick interface; the Next joystick ports; mouse.
Controller — map a host gamepad to the emulated controls.
Audio — master volume and the per-source (beeper / AY / DAC) balance.
Debug — which debug server to run (DZRP / ADP / both / none) and the ADP port.
Advanced — emulation-faithfulness toggles (all on by default): the 28 MHz SRAM read-wait, the IM2 hardware daisy-chain vector, and an optional CPU-speed cap. Leave these unless you’re diagnosing a specific divergence.

Preferences — General tab Preferences — Media tab Preferences — Display tab Preferences — Input tab Preferences — Controller tab Preferences — Audio tab Preferences — Debug tab Preferences — Advanced tab