“STP” in Project window > Advanced Upscalers by Priority menu list is shown as available to add when it is already added to the list

Thank you for reporting a bug to Unity. We have reviewed the issue carefully, and in this case, the team is unable to prioritize fixing this bug. There are a number of reasons we make this decision, including the impact and severity of the issue across our user and customer base, and the possibility that future plans may solve the problem in a different way, or that a workaround for the bug may be available. Today we will be closing this case. Thank you again for taking the time to report this issue, and please let us know if there is anything else that changes the impact or severity of this issue.

Unity 6000.2 has reached its end of life and will not receive further updates. If you need additional fixes, please upgrade to a newer Unity version.