I feel you! I'm so sorry for your losses - your story sounds very similar to mine, I've had 4 miscarriages since we had our four-year-old and when I got pregnant the last time my partner and I agreed that it was our final shot, and we wouldn't try again. Sadly that pregnancy ended in miscarriage at 13 weeks, so here we are.
I don't think the other people who have replied really understand what you're asking - it's not useful to say 'just relax/stop tracking and see what happens' because it is actually quite painful to be stuck in that holding pattern of 'could I be pregnant' month after month, however hands-off you are about tracking. And, of course, when you've had multiple losses you know that falling pregnant is not necessarily a totally happy occurrence. It's signing up to potentially losing another baby, going through those horrible weeks of uncertainty, hope, fear, and grief. It's a tough thing to put yourself through.
So, yes, I can understand why you are saying that there must be an end point.
It is empowering to take matters into your own hands. I would give yourself a deadline, after which point you will stop trying and instead work towards being at peace with your one lovely child. For me, I realised that the potential age gap was growing larger and larger - so the family life I'd imagined, with 2 or more kids close in age, was never going to happen. Not that it wouldn't still be lovely, but at this point I'm enjoying being out of the baby stage, being able to easily take our daughter on all kinds of adventures, not worry about naps, knowing that all our resources can go to her.
For me the right choice is to stop now. It's better for my mental health to draw the line and move on to the next chapter. For you, the answer might be to try for another year, or to commit to investigating certain tests or treatments. I don't know what that boundary will look like for you. But I think you are right to want to be intentional about it. You can't go on forever thinking 'maybe this is the month', or wondering if your family is in its completed shape or if there's another child still waiting in the ether. It is such a helpless thing, infertility, that anything you can do to take some control is really important.
Good luck! I'm sorry you and I are both walking such a hard road, which can be so difficult for other people to understand.