Pre-installed partition, what to do with it?

coolnewyorker said:

So, now I know there are two partitions (1 and 4) and they occupy a lot of space ... and they are empty. What are they in there for? Should I delete them?

They are not empty. They only appear to be empty because Disk Management does not have the required permissions to see their contents.

Other tools, such as MiniTool Partition Wizard, will tell you that they're actually quite full.

coolnewyorker said:

So, I presume the necessary data to reinstall W11 are kept in these partitions? I just reinstalled my OS two days ago (because I had messed it up with too much tweaking). I opted for cloud source instead of my device. I understand cloud download uses more than 4 GB. Is it better? BTW, should I install mini tool Partition wizard?

There are many ways to install or reinstall Win 10 /11.
For reinstall you can do a reset
To install from scratch, that is, you clean the drive first and install from a USB drive, you do a clean install
I suggest you build the USB Win 11 22h2 installation drive using MCT

The Mini Tool Partition is a very good tool to manage drives and partitions.
As you can see you only have one drive with 4 partitions and 8G of unallocated space
- EFI is where you find the boot manager on a GPT drive. Normally it is 100M and Fat32 formatted and has no letter assigned to it.
- MSR is a small partition (16M) created by Windows. Nobody really knows what is it for.
- The C: partition, NTFS formatted. Is where you find Windows
- The Recovery partition, NTFS formatted. Is where you find the recovery environment and has no letter assigned to it.

You can add the 8M unallocated space to the recovery partition.