Poplars are notoriously unreliable trees. If you see any defect in the cambium it will surely turn into a risk. Rip it out and plant a more robust species.
You might find that it’s not a crack but decay that is hidden behind a sheet of bark. Looks like there is a live edge to the left so I’d look for loose bark to the right. Not much you can do except evaluate if it is in danger of damaging anything if it fails. If so it’s gotta go.
In Italy on vacation with the wife walking around a well maintained park. All of the big trees have heading cuts. Some of these trees are very large and look like this is an annual thing. My only guess is it’s to maintain spacing between them. Maybe the rules are different here…