> When we want to talk about their solution in the interview, they “can’t remember” how it works or why they picked their method.

Sweet! That sounds like perfect signal for "used ChatGPT" to answer this question. So, you can send take home test, candidate sends reply (many from ChatGPT), then you do quick follow-up phone/video call to discuss the code. When you get the "signal" (should be quick!), then you immediately close the interview and move to the next candidate.