- First Question -
It is correct, but it sounds weird.
1. Playing video games for a long period of time can cause a lack of sleep.
2. Video game addiction can cause a lack of sleep.
You should use "can cause" because not everybody sleep will be affected by playing video games.
- Second Question -
It is correct with a small correction
1. Drinking milk before going to bed can boost your sleep quality.
2. Drinking milk before going to bed can boost the sleep quality of an individual.
Good luck with your studying !