As I spend a lot of time researching my seeds can I block them with a black rectangle so people don't know what seed I am using and can't replicate run?

Short answer: No.

Long answer: Even though speedrun records are milestones for individuals, speedruns are a community project. They are built on community knowledge.

This is evident in many speedrun communities where players livestream their process of testing out new tricks, and even publish video tutorials about them, before they manage to grab the record.

Once you make a run, everything you did will be public and available for other players. (And it is important for verification purposes that you don’t hide anything, even inadvertently.) Likewise, don’t pretend that you don’t use any knowledge accumulated from other players either. If you accomplish a record, that is your reward, having the best leaderboard position.