It's more a "harem" in the sense that most of the major characters other then the MC are female. The MC is constantly surrounded and interacting with witches (which are all female characters) that feel indebted to him because he's making his kingdom a safe place for them while everywhere else is trying to burn them at the stake. But there isn't really any romantic feelings involved in his relationship with most of the witches. So not really a true harem per-say. There is, however, a bit of a one-sided love triangle. There is two witches that have romantic interest in the MC and the MC very obviously only holds romantic feelings for one of them.
Now for the "is it good" question. This is a kingdom-building story and it does a fairly good job and doing that. I wouldn't call it a masterpiece but it has decent pacing and little twists here and there that keep things interesting and moving along. I think the best part is probably the world-building. I really like the lore they are building up and was rather impressed with the reveal behind the church's reason for its actions. It actually makes sense instead of just being the usually boring "use god as excuse to be bigot".
I'd say read a couple chapters to get a feel for it and if the interactions with the girls don't annoy you too much you're good to go. The tone is pretty consistent throughout so if you like the first bit you'll probably like the rest.
I second this but want to add that the story is solid, there is a LN for this and it's a lot more into the details of world/society building than the manwha. The artist of the manwha added some fan-service in the clothing and attitudes of the witches to the story for some reason, that is missing from the novel and frankly doesn't need it, but it also isn't interfering with the core of the story, which is not Harem. So the look is misleading.
Is this good? Like there's no red flags or something? Also is the harem okay here, I saw the genres and I saw Harem there so... ( I'm not really like harem. )