Can't decorate apartment for holidays

So my son lives in an apartment and it is currently harvestfest. I've placed a build and buy decoration for the decorations tradition, but can't place the other kind because they aren't allowed in apartments. I know this makes sense because you couldn't decorate the outside of an apartment realistically, but now my aim can't finish this tradition and it's just a bit annoying. The check mark is flashing rather than solid, I'm assuming this is because I've only done half of the tradition. A way around this would be appreciated!! And if there isn't one, maybe in the future it could be changed so that Sims in apartments only have to do the build and buy decorations to complete the tradition?

Thanks 🙂