I'm a big fan of closure and seek it actively, where I can. However, I would usually only apply it to more or less "single incident" things, like a breakup or loss of a job or loss of a friendship... Stuff like that.
I'm not sure I'd really use the word closure in the context of trauma... At least, not "capital T" trauma and not for C-PTSD... I think it's possible to gain acceptance and make peace with those things... Even if the road is long and it seems impossible... I know I've literally stood at that point and been 99.999% certain that I will not "get over" or "move beyond" the way my trauma has impacted me... Feeling certain that it would impact me that way for ever... But can definitely say that, say 10 years later, with lots of therapy and other support, that certainly did change... Still feels miraculous to me...
Currently, I'm dealing with adult trauma that occurred in 2016 and in the same loop again of "this will never, ever get better"... And yet it already has, by tiny degrees... It's not quite as bad as it was initially... And although I still don't *feel* that the rest of it will lift or change or go away... I know from the experience of working through childhood trauma that what seems impossible can, in fact, be very much possible. And I've heard the same from lots of friends and accquaintances with trauma...
Having said that, I'm personally not sure whether "closure" is a helpful word for major or complex trauma...
ETA: Personally, I think trauma that goes "dormant" or "silent" for many decades... You can't count those decades of not being aware of it as part of the healing process... I'd start counting "how long it takes" from the point where you actually enter a decent trauma therapy...