When playing a hand that won't score, it would be helpful to have some part of the UI show that your played hand is debuffed. Another option to consider would be adding a confirmation when taking an action where the hand will not score.
I've lost several runs to accidentally playing a 3-card or 4-card hand against The Psychic, which requires you to play 5 cards.
There is the warning shown at the top of the screen ("Hand will not score, Must play 5 cards"), but I typically ignore it. It first appears when you select one card to play, and it isn't relevant at that point (because you have more cards to play). By the time you finish selecting cards, you're looking at the Chips/Mult for the hand and the "Play Hand" button. I don't check the warning again because I've already "acknowledged" it in my mind, and it's no longer part of the UI I'm looking at.
This is not a problem for bosses that debuff cards instead of played hands, as the cards themselves are visually debuffed and it's clear that playing them won't score.
I would love to see a solution similar to how face-down cards are handled. The chips/mult are changed to ??? x ??? to signify that it's unknown what your hand will score.
In this case however, your hand would not score because of the boss ability. It would be helpful to see 0 x 0 in the UI, or perhaps just reusing the debuff ❌ on top of each box to signify that it's not being scored.
You could also consider putting a debuff ❌ on top of the "Play Hand" button when a hand would not score. This wouldn't disable the button, but merely show it as debuffed. There are still situations where you might want to play a not-scored hand, for example when you want to preserve your discards, and this would still allow for that.
For controller players (eg. Steam Deck), in this situation you could change the behavior of the X button to focus the "Play Hand" button instead of directly playing the hand to act as a kind of confirmation.