How to know exactly what they know of me?

Hi all, semi-noob on privacy here.

Basic overview of my privacy "setup":

\- Have used adblockers for +15 years

\- Not on any social media with my real name

\- Using Firefox with the basic privacy settings

\- Always opt-out of cookies (I'm in the EU so they have to ask for consent for this)

But,

\- I use Google as my search engine and have a gmail and YT account

\- Outside of what I mentioned I don't generally …

adblockers ask basic cookies firefox media name privacy privacy settings real real name semi settings social social media