Welcome to the Bunnings Workshop community @TrendyK. It's great to have you join us, and many thanks for sharing your project.
Hopefully, @DIYgals can share some feedback on how their deck has held up.
Was it just the muddy paw prints leaving dirty marks on the decking, or does the coating have water staining marks in it? We'll need to establish if this discolouring is in or on the coating.
For any dirt that is sitting on top of the coating, you might like to use Feast Watson 1L Floor Clean and a microfibre mop to make quick work of cleaning the area. In your first image, I notice there appears to be some variation to the timber's colouring before oiling, which has potentially shown through the final coating. If it is the underlying colour of the deck showing through the coating, then a re-sand would be needed, so the timber is all taken back to a bare surface. A deck sander is the best tool for this job as it gives a consistent finish and is a lot easier on the knees than a handheld orbital sander.
If you can let me know the exact product you've used, I can investigate why the decking might discolour from the rain.
We have used an oil to finish our deck, and although initially it required quite a few application we are very happy with how it has held up. Our backyard is currently a building site, so it has copped quite a beating! @TrendyK what do you have around your deck? Our deck is surrounded by grass, I think this might also help with cleaning our puppers paws before she hops onto the deck.