Adulthood would be great for people if they didn’t have to work to be honest. Work in hunter gatherer days used to be getting the kill for the day and then hanging out around a fire. There is no way that translates to dealing with 8 hours a day of office/labor work. We exchanged all of that freedom for medical advances is fundamentally what it seems like in the end. Was it worth it? Sure, but this is definitely not the end/steady state.

Work is indeed the main problem. It doesn't need to go away entirely — in fact I think some amount of work is on the whole beneficial, but the status quo is clearly not sustainable. It's not reasonable to expect people to burn away the overwhelming majority of their lives just staying afloat and not become depressed and burnt out somewhere along the line.