Installing Linux into a Windows 10 computer using the Linux partition manager...without risking data loss.
Vice versa - Windows into Linux. The video fellow said use specific version 'EN_US_Windows_10_IoT_Enterprise_LTSC_2021_x64_DVD' for security's sake, and that it's free to use. I'm wary as this is the first I've heard of this.
When duel booting, are demands on resources increased, does the non-active OS run minimally in the background or does it stay totally off until rebooted as Primary?
Shakin' in my 'boots' trying to avoid mistakes.
You can only boot one at a time. When you run one the other day is just files on your hard drive. Before you install make a backup image to a USB HDD. I use rescuezilla which is free and simple to use. When I install Linux Mint it gives you the option of installing side by side with your existing OS or deleting the existing OS. If you choose side by side it handles the partitioning.
If you are that worried you should install Linux to a bootable flash drive using Rufus and boot Linux from the flash drive for a while until you feel comfortable
In a dual boot system, you run one OS or the other OS, but not both. No background, no resource sharing. The booted OS gets everything, the non-booted OS is completely off, gets nothing. No resource hit.
That's in contrast to using one OS as a host and a second OS as a virtual machine (VM). The two OSes are running at the same time, so resources are shared.

Thanks to MikelTackNailer for the ping!
I downloaded Windows 10 IoT Enterprise LTSC 2021 from...
https://archive.org/details/en-us_windows_10_iot_enterprise_ltsc_2021_x64_dvd_257ad90f_202301
...and got a license key for $9.99 from...
Burned the Windows ISO to a bootable flash drive with Rufus, booted from it and followed the directions.
I will try the Rufus + Windows 11 usb "hack" tomorrow. This alters Win 11 so that it no longer demands a Microsoft account to install it. Seems to also allow Win 11 installs on unsupported computers. Details at your favorite AI.

Yup, one wrong move and I'm zipped out of my shit. I hate this.