It’s a fine line, but it comes down to this: it’s not OK for the baker to refuse to bake a cake for someone in a protected class.
However, it’s also not OK for someone in a protected class to compel speech from the baker.
Ask the baker to bake a plain cake with no messaging on it: the baker can’t refuse on the basis of any protected attributes, like the customer’s race, etc.
Ask the baker to decorate the cake with a “happy pride day” message? Only if the baker agrees to that expression. You can’t compel speech.
It works the other way too: you can’t compel the baker to write something they disagree with if they don’t want to. It’s clear why a baker would be within their rights to refuse a “I’m glad all the Jews died” message on the cake. The baker is within their rights to decline any expression they don’t like. And that’s the way it should be.