How to reboot in Safe Mode? Holding in the power buitton doesn't work

You will likely need to perform a DFU firmware Revive. This may allow the Mac to boot normally, but if it still won't boot normally, then you should at least be able to access the Options screen. You may need to perform the DFU firmware Revive again if macOS failed to boot. I have encountered some of my organization's M-series Macs getting only one chance to access the Options boot screen after a Revive procedure. Sometimes getting the M-series Mac into DFU Mode can be tricky.

Maybe you can give us some more details on what happened prior to needing to access Safe Mode?

Also, what version of macOS are you using?

Try disconnecting all external devices except for a single display and your keyboard & mouse/trackpad just in case an external device is causing a problem.

Edit: Forgot to include the link to the Apple article with instructions for DFU firmware Revive:

How to revive or restore Mac firmware - Apple Support

Next step to try is Recovery.

Use macOS Recovery on a Mac with Apple silicon - Apple Support

if this will not load, you Mac likely needs a firmware restore or a service visit.

How to revive or restore Mac firmware - Apple Support

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there's a bit more to the process on Apple silicon Macs

Start up your Mac in safe mode - Apple Support

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you can try this laundry list, then you are out of 'ordinary' options:

If your Mac starts up to a blank screen - Apple Support

Thanks for the update. Hope the rest goes well now.