Requesting advice on helping parents

I recently graduated university and had to move back in with my parents until I find a full time job. After years away from them and being 27 years old now, I realised I have always been cleaning up after them since a young age - I just forgot about it after being away.

Since I moved back in, I've tried to help them let go of things by explaining that we cannot keep everything in life and that we must only keep what we truly value, and what we reasonably have space for.

Both with and without them being present, I've tried to sort through stacks of grocery receipts, 10 years worth of bank and credit card statements, a collection of 150 received birthday/xmas cards (common to receive many greeting cards in the UK), 50 gift bags, maybe 50-70 pairs of shoes between them, there are around 60 different cleaning products under the sink. All of the drawers under my bed and half my wardrobe is filled with my mum's clothes, I don't have a single personal item anywhere in the house other than my room, I'm not even able to have 1 entire room to myself in the house due to the volume of stuff they have. Every time I open another cupboard or drawer to look for something, my heart sinks to find more unnecessary (to me) clutter and even things retrieved from the trash I have tried to throw out.

It's not a house you walk into and immediately think "this is a hoarder's house", and I don't know if I am being insensitive by posting this on this subreddit, because you can walk around the house and things like walkways are clear, but it feels like I'm cleaning up after grown adults constantly and it's really upsetting that they live this way, and has brought me close to tears a few times.

My biggest issue: my mum and step-dad sleep in separate rooms and my step-dad's room shares a wall with mine, and his room smells so bad like damp/musty from excessive amounts of furniture and a wardrobe packed full. He keeps his door closed, I think because he is embarrassed about the mess, and I think the smell is coming from mould in the walls, and it's spreading to my room.

I try to ventilate the house by opening windows, declutter, clean, try keeping the house a good temperature so it doesn't get too humid. I'm trying to make the house a nicer environment to live in, but my actions just seem to frustrate them.

Am I fighting a losing battle, is there anything I can do, or should I just focus on moving back out again as soon as I can?