No idea why this happens, but when I try brewing coffee with any of the special ingredients (blaze powder for strength, for example), I get a coffee with no effects. And not only that, but it doesn't even consume the ingredient. Kinda makes the coffee machine pointless.

Can confirm this is the case with 1.2.14.14 for 1.20.1, under Forge 47.4.0.

Nothing that is added in the additional ingredient slots on the right in the coffee machine UI gets added to the coffee brewing process, making only black coffee with no special effects.