I'm so sorry. Sometimes you wish they could just tell you!
I found this "guide" (or at least the chart you fill out on the last page) to be incredibly helpful, or at least get you thinking about things. Our vet shared it with us when we had to begin thinking about difficult decisions. Good luck to you!
https://vmc.vet.osu.edu/sites/default/files/documents/how-will-i-know_rev_mar2024ms_0.pdf