macos big sur cannot be installed on macintosh hd

What file system is on the macOS boot drive? Big Sur requires the boot drive to be formatted with the APFS file system. In theory it should be possible to convert the MacOS Extended file system to APFS, but I'm not sure it works with Catalina or Big Sur (you need to be booted into Recovery Mode or from a USB installer -- other users have mentioned in posts that they could not convert the file system with Catalina/Big Sur). If your macOS "Macintosh HD" volume is MacOS Extended (Journaled), then you will need to use the following instructions to attempt to convert the volume to APFS so that you can proceed with the Big Sur install.

1. Boot into Recovery Mode using Command + R or Command + Option + R
2. Launch Disk Utility
3. Click on the "Macintosh HD" volume and click the "Unmount" button on the right side
4. In the Edit menu select "Convert to APFS"
5. Quit Disk Utility once the conversion has completed.
6. Install Big Sur.

(source: https://discussions.apple.com/thread/8613766?answerId=34115706022#34115706022 )

If the "Macintosh HD" volume is already an AFPS volume, then check to make sure you have at least 36GB of free storage space on the drive.

If you meet both of these requirements, then boot into Safe Mode and try running the installer again just in case you have a third party app installed which is interfering with the normal operation of macOS (anti-virus apps, cleaning apps, third party security software are known to cause problems).

If this laptop is being managed by your school or employer, then perhaps they have blocked the ability to upgrade to Big Sur. Check with the IT department for assistance.

If you have at least 55GB of free storage space available, then you can try installing Big Sur from Internet Recovery Mode (Command + Option + R) or from a bootable macOS USB installer.

Make sure to have a good backup before attempting to convert the file system and before attempting to upgrade macOS just in case something goes wrong.