Yes, the OS is on the drive right now. The unit comes with Windows 11 Pro preinstalled on that drive. If you clone it to the new drive, then the OS will be on the new drive too, and you can then replace the existing drive with the new drive.
Make sure to set the system up with the existing drive first. Meaning the initial Windows setup steps you have to go through when you start the unit, then the Windows updates and all that to bring it to current. You want to first set everything up as if you're going to use the unit as is, as in not upgrading the drive. Then, once you've done all that, you can clone the system from the existing drive to the new drive. Then replace the existing drive with the new drive and the system will then run off of that new drive, which will have an exact copy of what was on the drive the unit came with.
Or, you can do it the way I linked to, where you would install Windows from scratch on the new drive, but you would do that AFTER you've set up the system with the existing drive and signed into your Microsoft Account for the sake of system Activation, and after you've saved the driver folder from the existing installation, as you'll need to install some drivers after the clean install on the new drive.
This is more info on the clean install process, including a link to a guide on how to do it if you're not familiar with the process.
Whichever you do, just make sure not to wipe the existing drive, or at least not for now, as you want to first make sure the new drive is working as it should for a system drive. This way, if anything goes wrong, you'll always be able to reinstall the drive the unit came with, which will still have the system and will still work with the unit.
For reference, you'll need a USB to NVMe adapter in order to be able to clone the system from the existing drive to the new one. If you don't have that, I'd just go with the clean installation of Windows 11 Pro on the new drive, but make sure to read about the process if you're not familiar with it. And again, remember to save the driver folder from the existing system drive, which is in C:\Windows\System32\DriverStore. The folder you want to save is 'FileRepository'. You can just save the entire folder rather than each of the files within it. It'll be about 2.5GB to 4GB in size, so make sure you have enough room on the USB flash drive or whatever else you save it on. You'll use these saved drivers after the clean install, as Windows will need some drivers after install that you may not be able to get through Windows Update. It's also just a good idea to have a copy of the drivers on hand, in case you ever need them.
Lastly, if you're very new to cloning or clean installs and you're not very comfortable doing it, I'd have someone help you, if you have that option available.