Hi and thanks for reaching out. My name is William. I'm a Windows technical expert. I'll be happy to help you out today.
Normally, this setting is toggled via group policy so I am wondering if you may have connected your device to your work or school via the Accounts panel > Access work or school. If so, you may have glossed over the prompt that asked if "Allow my organization to manage my device" and selected Yes. Doing so can lock out or prevent certain settings from being accessed or changed. You can undo this by removing the work/school account > restarting > and adding it back (if necessary) and selecting No to the prompt.
If the above is not the case, then open regedit.exe > go to Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender Security Center\Virus and threat protection and delete UILockdown is it is present (if it equals 1, that means the "Virus and Threat Protection" panel is being hidden). in fact, you should delete the entire Virus and threat protection key if it contains any other values.