Ah – the screenshot helps!
It looks like you are using the “main” branch of oopsy. The support for custom seed boards isn’t part of that branch yet, but you can get it by working from the “dev” branch.
To grab that, clone the oopsy repo into your Documents/Max 8/Packages (delete the old oopsy folder first) and then use git command line or a git app to switch to the “dev” branch.
More info here: How do I get the dev branch working? (never mind, got it)