Up In The Sky is canon, yes.
When UITS originally started being released(which was before the conclusion of Doomsday Clock), the main reason its canonicity seemed questionable is because Clark was shown having a convo with Pa Kent:
https://i.imgur.com/oIl0UnG.jpg
And at the time, Pa had been canonically killed in a car accident back when Clark was still in high school:
https://i.imgur.com/IuWWEK9.jpg
https://i.imgur.com/jNYJccN.jpg
https://i.imgur.com/7t4qyM2.jpg
https://i.imgur.com/mQCK4EI.jpg
However, the final issue of Doomsday Clock retroactively altered Superman's history. So now, in current canon, Clark saved Ma and Pa from the accident:
https://i.imgur.com/4CqJjVg.jpg
https://i.imgur.com/L6fKRKZ.jpg
And they are still very much alive:
https://i.imgur.com/k9JLtfj.jpg
Which means there is no longer a reason to doubt UITS's canonicity.
UITS when it concerns power levels are all over the place. There are some amazing parts of the story and there are some outright terrible parts of the story. It's a win/lose situation when using anything from that story. Remind me of the inconsistency in the Jean Grey Phoenix story. Great read but inconsistent power levels.