It's like this, which is probably what the court will decide:
You cannot discriminate by refusing to serve a protected class BUT you should not be forced to use your artistic or similar professional talents to make or desed thsign something that is against your religious beliefs. If a cake baker refuses to sell a cake in their store to, let's say, a gay couple, that is discrimination. But, if that gay couple wants the baker to make or design a cake and the requested design is clearly against their religious values, the baker should not be forced to do this. The baker should also be able to prove that this is actually against their religious beliefs and that they aren't just simply claiming that in order to discriminate. In other words, you can't just be claiming this exemption when you can't prove you actually have those religious beliefs.
To expand further: In most cases I cannot see an establishment being able to discriminate against a party due to protected classes and that goes both ways. Say a restaurant provides services for a large group but those services do not include artistic talents, merely providing food and drinks, so, Christians would not be able to discriminate against LGBQT+ and vice versa.