Yes, it does. Do NOT listen to people who say that senior year doesn’t matter at all.
It’s one thing to lighten your coarse load a bit from junior year to senior year. It’s another to go from taking 5 AP classes during junior year to only taking easy electives during your senior year - they will care about that.
and about the GPA thing, it depends. If your apps are due sometime in January (regular decision, probably), there is a very high chance that they’ll consider your senior course load along with midyear grades. If you do Early Action/Early Decision/Priority (November-ish), they won’t - but they will probably require that your school sends midyears grades (when available) and they can rescind you if your grades slip too much - it has happened to people before and you don’t want it to happen to you.