New computers will get Windows 11 first and existing Windows 10 devices will get the upgrade for free via Windows Update before mid-2022. Microsoft doesn't specify whether it will be possible to get the upgrade for free before 2022. Typically, Windows users can force the installation of a newer version before it's automatically pushed via Windows Update.
There is one caveat though. Windows 11 has higher minimum system requirements than the current version of Windows 10 -- so a lot of users with older computers will have no upgrade path. If Microsoft keeps insisting on TPM support, a lot of users will be left out in the cold.
Starting with Windows 11, Microsoft plans to switch to just one feature update per year. Up until now, Windows 10 got two updates per year.
Windows 11 is due out later in 2021 and will be delivered over several months. The rollout of the upgrade to Windows 10 devices already in use today will begin in 2022 through the first half of that year.
— Windows (@Windows) June 25, 2021