What do you do if a folder with a "?" appears, and command-option-R doesn't take you to installation?

• If your Mac starts up to a question mark - Apple Support

https://support.apple.com/en-us/HT204323

"..A folder with a flashing question mark means that your startup disk is

no longer available or doesn't contain a working Mac operating system."

Of two-sections, second part suggests

"..If the question mark persists, follow these steps.."

1. Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off.
2. Turn on your Mac and immediately press and hold Command (⌘) and R to start up from macOS Recovery.
3. While in macOS Recovery, use Disk Utility to repair your startup disk.
4. If Disk Utility found no errors or repaired all errors, reinstall macOS.
5. If you still need help, please contact Apple Support.

The section about startup from macOS Recovery includes what you ask.

Others are there for troubleshooting the symptoms.

What year MacBook Pro?

See trouble-shooting tips in this document by clicking here --> About macOS Recovery on Intel-based Mac computers - Apple Support