Compress Windows folder?

Can I compress the Windows folder or at least the Winsxs folder? Like right clicking, and under attributes> compress without any harm to the system?

No....and compressing the Winsxs folder is not smart. Pretty much everything in Winsxs is a hardlink. You alter those files you alter everything that links to those files. Also the size reported in folder properties is incorrect and inflated.

Ok, then is there any way to reduce the size of the Windows OS on my drive?

For starters I would delete the hibernation file. Use this command in eleveted Command prompt: powercfg -h off . That will save you a few GBs. What are you trying to accomplish? You can uninstall programs you do not use or slipstream the whole installation disk. There are many ways.

Hibernate - Enable or Disable

Well I cant do that, because I'm on a laptop, and use it because i only turn it off if i need to restart, otherwise i hibernate.

Then my only recommendation is get a bigger drive.
Using Windows Compression on anything on the drive (in my opinion) is a bad idea.

I have seen many corruption issues when trying to go back and uncompressing.
Especially when someone doesn't realize what they are doing and they don't have enough space to uncompress and the data blows up. literally, and you lose it.

No, because I dont want it to drain my battery, even a little bit.