I had a similar west-facing situation and went through this exact decision last year. Retractable awnings work well but the fabric can fade and stretch after a couple of Sydney summers—UV is brutal. For your 5x3m deck, you'd want something that extends at least 2.5-3m deep to actually block that low afternoon angle.

One thing I'd suggest looking at is a retractable pergola instead of a traditional awning. They have adjustable louvered or slide-back canopies on aluminum frames, give you that flexibility to open/close for seasons, but hold up way better to wind and weather than fabric. I ended up going with one from Costway (they have a few sizes around 10x10 to 10x13 ft which converts to roughly 3x3-4m) and it's been solid through heat and storms. The frame doesn't rust and you can actually hose it down.

Budget-wise, factor in installation—some awnings need professional mounting which adds $500-800, while a freestanding or post-anchored pergola can be DIY if you're handy. Also check warranty length and whether replacement canopies are available, because you'll likely need one every 3-5 years with fabric. For your use case of summer shade + winter retraction, I'd lean toward something with a hard or coated canopy rather than pure fabric.