Microsoft has tools (e.g. see ‘PC Health Check’ above) which will say whether a PC is ready for Windows 11, but some tools may say that a PC is ready, whereas other tools may say the opposite. You may have to try to install Windows 11 to find out whether you can.

For folks who can update, Microsoft will offer the update to all their PCs by mid-2024, though folks can opt to upgrade earlier, e.g. using https://www.microsoft.com/en-us/software-download/windows11.

For most folks who can update, it would be prudent to wait for at least several months — perhaps ¼–½ year — until Win­dows 11 becomes reasonably stable and feature-complete: the current version of Windows (DEC 2021) has quite a few bugs; Microsoft says that Windows 11 will be feature-complete by mid-2024.

For folks who buy new PCs, it would be prudent to buy PCs with Windows 10 installed, but which are Windows 11 compatible, so that the PCs can be upgraded to Windows 11 when it becomes reasonably stable and feature-complete.

For folks who can update, it will eventually be necessary to upgrade to Windows 11 simply because support for Windows 10 is end­ing in 2025; and it would be wise to upgrade to Windows 11 while the upgrade is still free; the upgrade will be free until at least Oct. 5, 2022.

Be cautious in updating to Windows 11, because it will break a few apps: if you depend on a particular app, make sure that it is compatible with Windows 11 before updating.

Be prepared to cope with jarring differences in Windows 11, e.g. with the new Windows Explorer icons used to cut, copy, paste, rename, share, and trash files.

For folks who upgraded to Windows 11 while it was still unstable and feature-incomplete, it would be prudent to check for updates frequently, e.g. once a week, and whenever an update appears in the news.

You may also wish to consult Wikipedia’s article about Windows 11.