No- you don't have to pay for an upgrade. However, if you want the upgrade and your computer is too old to run it- then you have to buy a new computer but the OS is always included in the price.
The biggest problem MSFT has is that businesses- which have licenses- do NOT like to upgrade and there are thousands of them and that's where a lot of pushback will come from.
For people who want a new computer but don't want Win 11, you can always buy one which you can configure yourself and choose the operating system. You still won't get the security patches, but some folks don't care.