Getting some shade over a young tree rarely hurts. You may want to make sure it gets full sun in the morning and late afternoon just to be sure it’s getting enough light as mango’s are full sun trees. Some mango’s seem to take longer to establish than others. I’m not sure if it’s the rootstock or something else. My PPK had 1 growth flush per year for 2 years before it really started growing and my small 1gal Sunrise only flushed once or twice in its first year and is now growing like crazy. Other mango’s started flushing within a couple months of being in the ground. I’d let it chill in light shade for a while, make sure it gets water a couple times a week but don’t overwater.