is it l’halacha allowed to do bushiness with a catholic church? like providing them with IT systems or phone service?
Yes, this is not providing them with material for their worship, which would be a question of lifnei iver, rather doing business and making money. The church would continue to function with or without you, and find another service provider, so that you are not keeping them open and running with your business.
There is no prohibition doing business with the church for your own benefit in a way that is not directly supporting the church and is insignificant to the church [i.e. your business will not effect it’s opening or closing or running in any way]. The issur of doing business with non Jews who will use the money for their Avodah Zara, which we find in the first perek of Avoda Zara is because of Lifnei Iver as you are directly causing them to thank their psalim, that is why this is only within 3 days of their holidays. Here there would not seem to be any lifnei iver.