While Norton advertises support for "Norton Security" in the "Privacy Monitor."
Searching the internet I see other sites that "say you can opt out" of data mining. I would imagine that anyone doing this would need to signup and leave information that you trying to keep unknown/private and defeating the purpose.
Is there any reason to expect these sites to be valid? If not. Are there any valid sites to optout of and recieve results?
I noticed that no one has replied to your question so I'll jump in and throw out a few comments while you're waiting for one of the Norton 360 users to respond. In the mean time you might want to read SoulAsylum's Verizon Wireless Customers Please Read that was posted today in the Norton Tech Outpost on the topic of automatic opt-ins.
Do you have a Norton 360 product like Norton 360 with LifeLock Select or Norton 360 with LifeLock Ultimate that includes the Privacy Monitor described at https://us.norton.com/feature/privacy-monitor that will scan popular data broker (people-search) sites to look for your personal information in their database, or were you thinking of adding the Privacy Monitor Assistant to your Norton subscription for an extra fee that will submit opt-out requests on your behalf (sorry, I don't live in the US and don't use Norton 360 so I'm not sure what features are bundled with Norton 360 Standard/Deluxe/Premium these days)? LANI TB's 26-Oct-2021 thread Privacy Monitor notes that they were sent an email from NortonLifeLock offering a free Privacy Monitor scan of popular data broker sites, so I assume this was just a marketing email to try and induce Norton 360 users to pay an additional fee for the Privacy Monitor Assistant.
I found a few other paid opt-out services for US residents like PrivacyBee and DeleteMe just by googling for "opt out service for data brokers" (see security expert Neil J. Rubenking's July 2021 PC Magazine review at Abine DeleteMe Review) but I can't vouch for any of these paid services personally. I don't know of any free sites that will scan multiple data broker sites and compile a single list of data brokers that store your personal information. DeleteMe does have a do-it-yourself guide at https://joindeleteme.com/help/diy-free-opt-out-guide/ that will help you find opt-out instructions for several data broker sites, and a list of sites covered in a standard DeleteMe subscription is posted at https://joindeleteme.com/help/kb/sites-covered-with-deleteme/.
There are also lots of article like Consumer Reports' 2017 6 Easy Opt-Outs to Protect Your Prviacy and Tom's Guide 2019 How to Opt Out of Data-Broker and People-Finder Services that explain how to opt out of a few of the larger data broker services yourself if you don't want to pay an annual fee to a service like Privacy Monitor or DeleteMe, but most of these articles only apply to US residents. Whether you pay for an opt-out service or submit these opt-out requests yourself, I don't see how you can avoid giving these services and data broker sites personal data like your name, address, and phone number (or even highly confidential information like your SSN or credit card number, depending on the data the organization collects) in order to stop them from sharing or selling your personal data to third-party partners. You would have to read the privacy statements or FAQs of these opt-out services and data broker sites to see if they explain how any personal data you submit with your opt-out request will be used and how long it will be retained on their servers (see the PrivacyBee FAQ "Why do you ask for my personal information to create an account?" <here> for one example).
If you're concerned that your electronic email addresses, phone numbers or passwords you use to create user accounts on various sites (e.g., LinkedIn, Facebook, tech support sites like this Norton community, etc.) were stolen during a data breach then the free Have I Been Pwned (HIBP) at https://haveibeenpwned.com/ is a reputable site. See my 13-Feb-2021 post in lisianthus's Personal Data Checkers on the Web that explains how this site uses an algorithm call k-anonymity to protect your privacy if you use the HIBP page at https://haveibeenpwned.com/Passwords to check if the passwords you use in your online accounts have been exposed in a data breach.