Surface turns on and shows "Couldn't find a bootable operating system"
Check the Boot Configuration to try to fix this. On older devices, the Surface turns on and displays a drive icon with an X in the top right corner. When you turn on your Surface, it boots to UEFI (Unified Extensible Firmware Interface). If you see this, try the following steps for a possible solution. Check the configuration of your device:
How to use Surface UEFI - Microsoft Support
In the Security section, you can set or change your UEFI password, turn Secure Boot on or off, and change your Simultaneous Multithreading (SMT) settings. Typically, only enterprises will need to change security settings—the default, out-of-the-box settings will be perfect for most users.
Boot Surface from a USB device - Microsoft Support
For info about how to create a bootable USB drive for your Surface, see Creating and using a USB recovery drive for Surface. To download a recovery image for your Surface device, see Surface Recovery Image Download for next steps. Make this Surface start from a USB drive. For all Surface models.
Recovery Drive - Microsoft Support
Creating a recovery media is a proactive measure to ensure that you can quickly and efficiently restore your system in case of major issues such as hardware failure. This media can be used for bare metal recovery on the device it was created for, ensuring a smooth and efficient restoration process.
Recovery options in Windows - Microsoft Support
Learn about the recovery options in Windows. Find out how to reset your PC, go back to a previous version of Windows, or use media to reinstall Windows.
Boot Surface from a USB device - Microsoft Support
For info about how to create a bootable USB drive for your Surface, see Creating and using a USB recovery drive for Surface. To download a recovery image for your Surface device, see Surface Recovery Image Download for next steps. Make this Surface start from a USB drive. For all Surface models.
Create installation media for Windows - Microsoft Support
Learn how to create installation media for installing or reinstalling Windows.
Windows 11 and Secure Boot - Microsoft Support
Learn how to change settings to enable Secure Boot if you are not able to upgrade to Windows 11 because your PC is not currently Secure Boot capable.
“We couldn’t update system reserved partition” error installing Windows ...
To upgrade your device, you'll need to free up 15MB of space on the SRP using the appropriate method below, and then try the upgrade again. If you're updating Windows 10, you need to free up 13MB. Press the Windows key + R. In the Run window that comes up, type diskmgmt.msc and press Enter.
Windows Secure Boot certificate expiration and CA updates
Secure Boot is a security feature in Unified Extensible Firmware Interface (UEFI) based firmware that helps ensure that only trusted software runs during a device's boot (start) sequence.