Very soft lawn

I've just bought a new build that was complete in June/July last year. The grass is long in parts, a bit matted in others. The most annoying thing is the ground is very soft. I've stopped walking on it as i it is starting to look a bit muddy. I'm a gardening novice and would appreciate any tips please!
Also, I was thinking about getting a small compost bin. I'm wondering if these attract any undesirables? Ie Rats, foxes, bugs?

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