My husband and 12y/o daughter are both ADHD. Both on Elvanse.
Methylphenidate did nothing for either of them. For my daughter it just gave her godawful comedowns in the evening without any benefit in the day.
Lisdexamphetamine (Elvanse) worked from the first dose and continues to do so 2 years later. She takes it first thing in the AM and you can literally see it starting to act 20 minutes later. She visibly relaxes and gains processing capability.
It helps massively with the demand avoidance, because for my daughter it's the ADHD emotional dysregulation that makes her so demand avoidant.
Eating: yeah, its an issue. My daughter is 147 cm and 35kg, so lower end of normal BMI. She loooks skinny, but she's an athlete, so it's hard muscle skinniness. Her 6-pack is amazing! She doesn't want to eat at any time other than breakfast, but we've worked out ways of ensuring tha she does. She knows she has to eat like an athlete to build the muscle she needs for her sports. We do smoothies, flapjacks with seeds etc added, nuts (not at school!), protein bars and balls, and lots of milkshakes. Just letting her not eat isn't an option. High calorie snacky options like cheese and olives always go down well. Easy to eat is key. Steep learning curve on the food front!
Overall, medication has ben an absolute lifesaver. It baffles me why medication for ADHD is so stigmatised. ADHD brains can't be forced into working like neurotypical brains by a bit of willpower. Medication has levelled the playing field for my daughter. It's also been life-changing for my husband who masked his ADHD for 45 years. In the last 2 years his career has truly taken off and he's had 2 huge promotions (and pay rises), becasue he can finally focus his abilties.