Can't unenroll from the Insider program toggle is disable.

From your screenshot the page is offering the immediate unenroll, which on Windows 11 means a clean install of the current release. The toggle for stopping preview builds only works in some states, so here is what usually greys it out.

First, check Settings, Privacy and security, Diagnostics and feedback, and make sure Optional diagnostic data is on. The Insider settings can lock up when it is off or when a policy forces it lower.

Second, look for a policy. If the PC is managed (work or school account, Intune, or Group Policy), an admin setting called Manage preview builds can disable the control. You can check it in gpedit.msc under Computer Configuration, Administrative Templates, Windows Components, Windows Update, Manage updates offered from Windows Update. In the registry the keys live under HKLM\SOFTWARE\Policies\Microsoft\Windows\PreviewBuilds. If a value is set there and you are allowed to change it, removing it and rebooting often unlocks the page.

Third, the two clean exits. If the Stop getting preview builds toggle is available, turn it on and the device leaves the program when the next stable release arrives, with no reinstall. If it stays greyed out, the only supported way off right now is the clean install that screenshot describes, so back up first and use the Windows 11 installation media.

If it still stays locked after checking those, tell us which channel you are on (Canary, Dev, Beta or Release Preview) and whether the PC is managed, because the answer changes between them.