Why do I have a "HD" in my bootcamp screen and not macOS or similar
The icon label is stored in the APFS volume Preboot in the same container as Big Sur.
The steps to change the icon label for Big Sur (macOS 11.1) is given below. Some of the steps are unique to Big Sur. Therefore, the steps may need to be adapted before being applied to previous versions of macOS.

While booted to Big Sur, get the name of the startup disk. From the menu bar, select →About This Mac. A popup similar to the one shown below will appear. In this example, the name of the startup disk is MyBigSur.


Next, you will need to boot to built-in macOS Recovery for Big Sur.

For Mac computers with an Intel processor:
From the menu bar, select →Restart….
Press and hold the option key immediately after your Mac begins to restart.
Keep holding until the Mac Startup Manager icons appear.
If your Mac is using a firmware password, you're prompted to enter the password.
Press the ⌘+R key combination.
If requested, enter the password for an administrator account.

For Mac computers with Apple silicon:
From the menu bar, select →Shut Down….
Press and hold the power button on your Mac until you see “Loading startup options.”
Select Options, then select Continue.
If requested, enter the password for an administrator account.



From the menu bar select Utilities→Terminal. A Terminal application window will appear.

Enter a command whose output can be used to determine the APFS container identifier and the APFS volume group UUID for the startup disk. Below is the command used in this example.

Note: Replace name MyBigSur with your own value.

diskutil info MyBigSur | grep -e Group -e &quot;APFS Container&quot;

Below is the example output. From the output, the identifier and UUID can be determined to be disk1 and 99740195-F728-458E-85A4-2E42A7932CB4, respectively.
   APFS Container:            disk1
   APFS Volume Group:         99740195-F728-458E-85A4-2E42A7932CB4


Enter a command whose output can be used to determine the identifier for APFS volume with the name Preboot. Below is the command used in this example.

Note: Replace identifier disk1 with your own value.

diskutil list disk1 | grep Preboot

Below is the example output. From the output, the identifier can be determined to be disk1s2.
           2:                APFS Volume ⁨Preboot⁩                 297.6 MB   disk1s2


Enter a command to mount the APFS volume with the name Preboot. Below is the command used in this example.

Note: Replace identifier disk1s2 with your own value.

diskutil mount disk1s2

Below is example output.
Volume Preboot on disk1s2 mounted


Enter the commands that will change the icon label. Below are the commands used in this example to change the icon label to macOS 11.1.

Note: Replace directory 99740195-F728-458E-85A4-2E42A7932CB4 and icon label macOS 11.1 with your APFS volume group UUID and desired icon label, respectively.

cd /Volumes/Preboot/99740195-F728-458E-85A4-2E42A7932CB4/System/Libary/CoreServices/
bless --folder . --label &quot;macOS 11.1&quot;
echo -n &quot;macOS 11.1&quot; &gt; .disk_label.contentDetails
chown :wheel .disk_label*


From the menu bar, select →Restart to restart the Mac.


References
Mac computers with Apple silicon
Mac startup key combinations
Use macOS Recovery on an Intel-based Mac
Use macOS Recovery on a Mac with Apple silicon