He sounds lost, OP, rather than anything more severe. If you've asked him to mow the lawn and he's doing it, in relatively good grace, that suggests to me he's perhaps just feeling overwhelmed and fearful of the vast amount of choices there are out there.
18 is a difficult age - officially an adult, but with no life experience and very little exposure to the world other than the bubble that you've grown up in. While uni is perfect for some, it's definitely not the right path for others, but it does give you insight into other people's lives and backgrounds which can be eye opening.
How receptive is he when you talk to him about the future? Does he shut you down and just repeats 'don't know' to everything, or is there some interest but then it fades when the answer isn't immediately there?
My eldest has always been laidback to the extreme (some say laidback, some say lazy - I'm on the fence). As we're both ambitious and really driven to succeed/progress/do well, we've struggled to understand his low-effort approach, but he's making his own way through trial and error and the odd gentle kick up the bum from us. He's now done a few months of a minimum wage job and while he's not loving it, he amazed me yesterday by talking about how long he needs to do this job for before he can move into an area with 'career progression'. I didn't see it coming, and it has yet to materialise, but have faith OP, he'll come good I'm sure.
A handful of thoughts:
Mowing the lawn - this can now be his job
Exercise - how can he move more?
Food - yes, keep feeding him but if you're working and he's not, he can cook the meals
Washing - nope, he can do this, and the rest of the household's too if you're out at work and he's at home.
Cleaning - if he's home, not working, he can keep on top of the housework. Don't expect him to see what needs doing, give him a list and let him work through it.
If he's resistant to any of it, then that's a different situation and needs more tough love, but I'd start with gentle nudges and carrots rather than sticks. But then I also know I'm a big softie...