[Ruminator]

mtp, once a parent- always a parent- true enough.

And you are obviously correct in that raising children partially shapes who a parent is as a person when done raising their children.
But to think that a parent owes you a lifetime debt or something for what you've contributed to who they are now as a person is screwed up logically.
They chose(hopefully) to create you. Are you glad to have a chance to live a life and make of it all that you can?

But as everyone else has told you; there are limits to a parents responsibilities toward their children. Otherwise the child would never learn eternally important consequences and responsibilities.
Are you going to pay them back in some kind of way for any hurtful results they've experienced in raising you since they owe you for your good contributions to them?

Each of you were/ are a source of blessing and hurt to each other. Thats just the results of human relationships.

By your logic, you forever owe any friend you make all of the support they need from you regardless of the horrific choices and consequences they make and bring upon themselves. Not true, life is way more complicated than that.
Enabling and codependency are very real and you can help someone to continue hurting themselves if you don't realize what you are doing. Read up on these at Wikipedia and elsewhere.

Also it was their own parenting choices and the consequences of those choices that has brought them, and you, to this point. If for the most part they made good choices toward/ for you, then you owe them gratitude. Just as I'm sure they are grateful for your good choices.
Likewise, as I mentioned above, it was also to some degree, your choices and the resultant consequences that has brought you, and them to this point in life.
They owe you nothing more than continued teaching and advice after you become an adult.
But having said all of this, just as a parent makes sacrifices out of love for their children when raising them, many that are beyond the required ones; a parent can choose to do so for an adult child of theirs; out of love, not requirement. But those enabling issues must be avoided.

* apologies- this post is off-topic of the OP