After receiving some feedback and suggestions, I've decided to split up posters, boards, and other wall decorations into their own separate Floor Builder category, Wall Decor!
In this category, you'll be able to find old and new wall decorations alike! Such as the new posters getting added to Baldi's Basics Plus in the 0.5 update.
And, as of posting this, there's already over 40 to choose from, and that doesn't even include the chalkboards! So you'll really be able to decorate your custom floor nicely with these!