I am just in the process of doing this.
Your PC on Windows 10 will continue to work after the deadline but it will not receive any further security updates after 14 October 2025.
How much of a problem this is, is up for debate and may depend on each individual user, what they use the PC for and how risk-averse they are.
Microsoft is offering extended security updates (ESU) for a period of 1 year. These may be 'free' (as in 'free lunch') or may be at a cost of £24.99.
This video gives a fairly good explanation of what is involved
https://www.youtube.com/watch?v=o4JBUCf8kMg
When I updated 5 different Win 10 computers I saw no option for paying or for using MS points. I just saw the 'no cost' option.
The catch of the 'free' option is that you have to sign up with a Microsoft account (which for many raises the issue of data privacy). The other 'gotcha' is that creating the MS account enables a feature to sync preferences on the computer to the MS account (undesirable for many who want to continue with a simple standalone PC).
The final 'gotcha' is the option to 'Make sure your PC is fully backed up' (mentioned in the video) which will sign you up to start using OneDrive (backing up data to the cloud). Here MS is trying to hook users in to its cloud storage services (again undesirable for many people) with the aim of dragging the customer into using up the free 5GB of storage and having to move to a paying option.
The video does a pretty good job at explaining how to sign up to get the ESU and then reverse the changes to go back to a local account.
I found there were numerous bugs and glitches in the process along the way (as is inevitable with MS). On one PC the login to my existing MS account failed and for several others they disappeared from the MS account once I had enrolled.