Intel Macs built between 2017 and 2020 carry a T2 security chip which, by default, forbids booting from external media. Recalbox PC therefore cannot start from your USB stick until that setting is changed.
This page is about Intel Macs only. Apple Silicon Macs (M1 and later) are not compatible with Recalbox: the PC image is an x86_64 image — see Compatible PCs.
Command (⌘) + R from the very beginning of the boot, to enter macOS Recovery.Utilities → Startup Security Utility.No Security, and tick Allow booting from external media.On restart, hold the Option (⌥) key until the available disks are displayed, then pick EFI Boot: that is your Recalbox media.
Your macOS installation is left untouched: at every boot the Mac goes back to macOS unless you hold Option (⌥).
The T2 chip also drives the built-in keyboard, trackpad and sound card of MacBooks. On some models these are not supported by the Recalbox Linux kernel: plan for a USB keyboard and controller, and an external audio output (HDMI or USB) if the internal sound stays silent. Community feedback, model by model, is on the Compatible PCs page.
To restore the original protection, repeat the same steps and select Full Security with Disallow booting from external media.