Almost everyone at some point in their life gets fed up and considers suicide.
Young people especially are susceptible for multiple reasons.
Causes of depression are many.
Elders often end up in a position in which their health is failing.
Their care and symptom(s) management become dependent on others.
Society likes to keep old people alive as long as possible because of the money being made.
I think nature provides a potential answer, or example to the question...when is suicide appropriate?
We are made of trillions of cells.
A cell has two functions (1) to operate as nature intended and (2) to duplicate itself.
When a cell knows it can not do that, it kills itself!
It is the natural order of things. Been going on ever since we were created.
We are energy manifesting in human form.
Our human form will slowly, in most cases, deteriorate over time for many reasons.
When our body can no longer survive it will die and we'll be back in energy form, whatever that may be.
Our consciousness survives.
Life on earth can be like being in a movie. We went to the movie for the experience it offered.
After the movie we go back to who we are.
If we don't like the movie, doesn't mean it had no value. Others may have loved it.
We can always go to another movie, get into a good book, a relationship, an experience, etc.
Maybe life on planet earth is like that? I don't know as I can't remember having a life before the one I have.
If I was curious enough I could perhaps find out via, past life regressions.
A few of the books at https://www.amazon.ca/s?k=many+lives+many+masters&hvadid=74766848077699&hvbmt=be&hvdev=c&hvqmt=e&tag=msncahydra-20&ref=pd_sl_66m2t15e37_e can give you an overview on the topic.
I think we are always supposed to be learning something. If you are learning you are living.
Maybe when we stop learning, might that be time to move on, without fear of consequences?