This seems to be a question of inscriptions, rather than the media upon which they are made.
Oddly enough, it might be perfectly biblical to inscribe a “bless you” cake (not blessing the “marriage” but the people).
We still could use religious freedom laws because the little snowflakes will use “civil rights” as cudgels.
Offer a price list with limited choices and leave out the one you don’t like. No custom offerings. Take our standard offering or go elsewhere.
Offer Genesis cakes and use the inscription about marriage from Genesis - works for Christians and Jews
No custom text available
And offer Koran cakes with what they say about marriage, I dont think they mention Peter marrying Paul
Offer flower cakes that customer can add his own inscription
Not a service offered by the bakery staff
We are not to bless those who bring a different gospel(2 John 1:10). Those promoting homosexuality are bringing a different gospel.
Also if we approve of the sin (agree, promote) we are just as guilty as if we committed it (Romans 1:28-32)