You have a couple of options. 1. would be to download the ISO directly from Microsoft, that's my preferred option if it's a licensed system or even if I am using KMS activation. Yes you need to used the media creation tool, just choose the option to install 10 on another system. I always use Rufus to tailor and create the USB stick for install on the system. Always choose UFEI if the target system offers that as an option in the BIOS..
2. if the target system has limited resources search the torrents for "Tiny Windows 10". Follow the directions included with the download. It will still need to be installed on a licensed system or a validation program such as KMS.
IMPORTANT: When dealing with KMS even before you attempt to download it on your sysem, disable Windows Defender including as a seperate action turn off "Real Time Protection" even after you disable virus protection. It can be found under Virus and Threat Protection --> Manage Protection. If you are planning on using KMS YOU MUST NOT SKIP THIS STEP. Defener will destroy KMS as soon as it detects it otherwise.