“Lacking Ownership”

My team has this one feature that we cannot seem to successfully deliver due t consistent failures or regressions in mandatory dependencies. Folks more senior than I have tried and failed; now this feature has been handed to me.

I’m really not happy about having to own this feature, but ever since coming to me my manager is insisting I show total ownership and get it done. I’ve gotten probably 75% of the way there, but the last 25% is really complex, in fact none of our tech leads can actually provide me a sound path forward.

Recently my manager has said that I “lack ownership” because I said it might be almost done, then a month later it wasn’t done for reasons outside of my control, eg dependencies having major regressions.

How can I best handle such a situation? I’m completely exhausted, but there is no way for me to get this off my hands.