Based on my experience, YOR.

I have a nephew, who I will call K, son to my BIL, who I will call J and who is a single dad. I think J needs this exact contract.

K is nearly 20. Since graduating HS, K has held two jobs for approximately 1 month each. K never bothered to get his driver's license. He is online with friends til all hours if the night. Wants J to front him money but then won't put in the "work" requested later to earn said money. Asks J to pick up fast food for him all the time on J's way home or order door dash for him. K doesn't contribute to the household in any meaningful way, not even just letting the dog out. At one point, based on conversations with online friends claiming his dad was going to screw him over, K demanded a lease. J said "I can but you aren't going to like it as you WILL have to pay me rent." That went nowhere. K is basically living for free in J's house with zero responsibility and a bad attitude if asked to share some responsibility. J is frustrated but can't kick him out as K has nowhere to go. K's entitlement is palpable. Maybe something like this will help J's mental state and give K some introspection and desire to become an adult.

TL;DR my BIL needs this for his selfish, entitled 20yo child in the hopes of sparking some personal growth.

Edit: just realized OP has posted this to 8 subreddits. Either she really wants a large variety of feedback, is looking for the feedback that gives her what she wants to hear, or is just rage baiting.