Hi Bill , the point your friend is trying to make is absolutely meaningless. There is no operating system in today's time which does not require it's installation image to be directly downloaded from cloud and then flashed onto usb drive for installation . If you are talking about Microsoft windows media creation tool which it uses for windows 10 and 11 and can be used to upgrade windows 8.1 to higher version please note that If you are talking about winds reset option in windows 10 where microsoft give you option to reset your system using windows 10 image freshly downloaded from cloud . what basically that image does it download that iso filed in temporary location ,extracts it and then windows reset menu after downloading triggers it with relevant setting which you choose and that's how your windows 10 get reinstalled ,during reset some services of your windows go into shutdown mode in order to be replaced. USB media installation is not an old style, microsoft still recommends installing windows fresh via USB installation media. Games you are able to play on other systems, depending upon if they are portable and their files do not require verifying installation from the registry or need to have dependency installed in order to play. That's what your friend did not tell you when he was telling you about how games are plug and play.. Operating systems on the other end are wholly different thing, they are the base platform through which your hardware runs and the very fac that you are able to write this mail to here. It's not necessary to use CD for installing and operating system you can use rufus to create bootable image and that file when you trigger install via installation menu gets copied to your hard drive, so that it remains on your system throughout your journey.and you can boot it and use it daily for your work without loosing data or having to plug in your os over and over again in laptop port. USB are storage limited os files require direct communication with something called hardware in order to use your network adapter and all, portable games do not require direct hardware interaction. All they use is your something called operating system's libraries to run. SO i don't know wether your friend does not have adequate knowledge or he is trying to make fun of you in front of public but the question you asked baseless . Linux like debian give you more option to customise your os by allowing you to select packages you want to install , it downloads those packages from internet and installs it on your computer hard drive. If you are asking about installing debain from cloud here are 2 thing that can happen. 1st worst case scenerio is that your winows os files gets replaced if debians installs it files from cloud while your windows is running and your windows 10 goes corrupt or become unstable and stiops working why? because The libraries which windows required for windows to run has been replaced or modified by linux install manager and is missing. boom , you just destroyed your own prefectly working installation of windows. 2nd scenrio is that you your are installing another os on top of your windows and all of a sudden that os loses communication to internet as that other os replaced it's network drivers while was also downloading os files also loses connection to internet , congratulations your both os are corrupt and not functional anymore and that is why we use USB installation media be it installing alongside or installing over other operating system
Regards
a windows 10 and Debain user