Look into Rufus, it will help you create a bootable USB with windows 11 and you can use it to do a upgrade or clean install from your windows 10 installation (clean install preferred IMO), it will even help bypass the hardware requirements and you can even remove the email account and use a local account. Make sure to use or write down your windows 10 activation/license for a clean install.

https://rufus.ie/en/

Guide: https://www.zdnet.com/article/how-to-install-windows-11-the-way-you-want-and-bypass-microsofts-restrictions/

That being said you could potentially still run the old wondows OS, but as time goes on new exploits could be found that can compromise the OS. If its behind a firewall such as your router its safer, but there is still the possibility of it being infected way off into the future.

Here is a video of windows XP running on a PC connected directly to the internet with no firewall. Its infected almost instantaneously. (Dont try this at home).

https://www.youtube.com/watch?v=6uSVVCmOH5w