Windows 11 enforces a pretty strict Trusted Platform Module (TPM) 2.0 and CPU requirement without which installation can get a bit iffy. Though there are ways to circumvent this, it either requires modifying the registry during setup or preparing custom installation media.
Microsoft has been cautioning from the beginning that unsupported PCs running Windows 11 may risk not receiving important updates. Now, the company is contemplating showing a watermark on the desktop for such installations.
Internal test builds, first spotted by Windows-enthusiast Albacore on Twitter, seem to indicate that Microsoft will soon have a watermark showing that the OS is running on an unsupported PC. The watermark reads "System requirements not met" but does not appear to cripple the experience in any way as of now. The message will also appear in the Settings app. Whether other system or inbox apps will also show such a message is not yet known.
At the moment, this watermark is being A/B tested in Windows 11 Build 22557 so all Dev channel users may not see it just yet. The desktop watermark can still be removed by modifying the registry. Just change the value of SV2 to 0 in HKEY_CURRENT_USER\Control Panel\UnsupportedHardwareNotificationCache and reboot.
Since this messaging is still being tested in the Dev channel, it may or may not make it to public builds. In any case, Microsoft wants to make sure you are abiding by their requirements in order to use the OS.