Hi @Boo13
The experience I had with my daughter whom was diagnosed with bi-polar and BPD - the nightmare years, the most difficult time was from the age of 15 to 21. Similarly to @Bunniekins's son. This change for the better happened recently (she turns 22 next April). We did have to make some tough choices to bring about her change for the better - some tough love was needed and she is now living out of home, but we are now closer with her respecting us. My daughter also suffered bullying at school, (much more serious than people are aware of, it really should be a criminal offence when extreme) -; and with her being too trusting, out of our care she was sexually assaulted and taken advantage of. She then also self medicated with weed and for awhile much stronger drugs and had three suicide attempts in that time and was scheduled - the latest attempt being near fatal.
With my own personal experience with my daughter and my own mental health issues, working and keeping busy with purpose is vital for improvement to mental health and self esteem/confidence/maturity. There may be some limitations to the hours and type of work depending on the severity of the mental illness but this was definitely good for her, and from what I have witnessed and experienced, good for mental health in general.
We encouraged our daughter to work - everything she wanted she had to work for. That motivated her initially. Now she could not stand the thought of not working. Some of those initial jobs did not succeed because of her issues and attitude to authority but she kept applying for other jobs - but now she has improved in herself and now holds down two quite stressful jobs for about a year now, not without its hiccups, but she is much happier when working. She does not then have time to dwell and feed her depression and anxieties, delusions, self doubt etc. Within 2 weeks of a near fatal suicide attempt one year ago she was back working for 10 hours to begin with in the workforce. All she could manage then until she got better but kept her foot in the door and gave her a sense of purpose.
If it were me I would encourage your son to "not give up" job seeking and career goals - and you would help protect his self confidence, determination, morale and self esteem by keep assuring that he will eventually land a job. Keep telling him that "he will succeed" if he keeps trying. A positive attitude and perseverance goes a long way to developing resilience in life - and this way you are helping him to be self reliant and to survive - you can protect him in this way. The worst thing I found I could do was "to do everything for her", "give her money without her earning it" and worrying over her too much. They have to get out into the world to learn on their own two feet - hard for a parent to watch, but with love and being for them when they fall we have to believe that it will work out for the best.
Helping to instil this confidence in him and encourage his drive will help him to not give into his depression as much. That's what I have witnessed under extremely adverse circumstances;, it really was against the odds - our daughter had her bad days but she got back up and as a result improvement has been made. This way you can help him by helping him to believe in himself and not let his mental illness define him or his dreams.
Mental illness can cause obstacles but does not have to stop us from achieving realistic goals (the movie "A beautiful Mind" is a good example) - even the noble prize is not impossible to sufferers.
My brother is paranoid schizophrenic and has worked off and on most of his adult life (he is 42). He can only work part time now because his mental health is declining but he is so much better and happier when working. The decline happened when he was unemployed for a lengthy period of time. It means much to him to work, to to be independent is very important to the little self worth his has. But they do need professional help to cope and deal appropriately with the paranoia. When my brother isolated himself when unemployed his delusions and paranoia became worse. I hope this has helped.