If you haven't upgraded to Windows 11 by October or removed all Windows 10 devices from your network, you could become vulnerable to cyber threats.
Regularly updating software to the latest versions means that you utilise any fixes for known vulnerabilities and security enhancements. Not updating means your devices and systems are not protected against the latest vulnerabilities.
Have a plan in place to check whether devices can be updated. If they can't, you need to make a plan for removing them from your network.
If you are a school or multi academy trust then review both the DfE Digital Leadership & Governance Standards and the DfE Laptop, Desktop & Tablet Standards.