Apple silicon Macs start up differently from Intel Macs. Everything is reached through one place: the startup options screen, which you get by holding the power button.
1Start with the basics
Restart the Mac. Disconnect accessories. Check for updates. Try a different user account to see if the problem is specific to yours. Many problems end here.
2Startup options
Shut down. Press and hold the power button (or Touch ID button) until you see Loading startup options, then let go. From here you can choose a startup disk, start in Safe Mode or open Recovery.
3Safe Mode
At startup options, select your startup disk, then hold Shift and click Continue in Safe Mode. Safe Mode checks the disk, loads only essential software and stops login items. If the problem disappears, a login item, extension or font is the likely cause. Restart normally to leave Safe Mode.
4macOS Recovery
At startup options, click Options, then Continue. Recovery lets you reinstall macOS (which keeps your data), use Disk Utility, restore from Time Machine, open Terminal, change Startup Security, and share the disk with another Mac.
# in Recovery Terminal or normal Terminal
csrutil status5Apple Diagnostics
At startup options, press Command+D to run Apple Diagnostics, which tests the hardware and gives reference codes you can look up on Apple Support.
6What doesn't apply any more
NVRAM/PRAM and SMC resets: Intel-only. Apple silicon handles these automatically, so a full shut down and restart is the equivalent.
Boot Camp: not available on Apple silicon. Use virtualisation apps for other operating systems.
Old startup key combinations such as Command+R at the chime: use the power-button startup options instead.
If the Mac won't start up at all, Apple describes a revive or restore process using a second Mac and Apple Configurator. Follow Apple Support for that, because a restore erases the Mac.