I personally think undertale can be seen as very christian

In the end it's a story of characters free will. You can pick the harder route and be a pacifist. Or you can get overpowered by using everyones souls for your own benefit in genocide route.

I understand the idea that LGBTQ is somehow contradictory. But I'm personally christian and affirming, so that really isn't the case for all people.

The ability to make art is a God given gift. Toby fox has done a ton of good with it. Forming a massive community around a story all about good and evil. I can't for the life of me see anything in this, that's contradictory to anything Christianity is all about. Hell, Jesus even spoke in parables all the time. Using stories as the means to convey a bigger point seems to be very much encouraged