Just call your dedicated wealth manager.

Your bank might ask you why you want 400K in cash versus a wire transfer or some other mechanism, but it's not "to approve of your reasoning". They might require some time to physically bring $400,000 in cash to the branch you're at.

I could, perhaps, see them wanting to be cautious if you appear to be having an obvious mental health crisis (but even then, as a paramedic I've heard more than one tale of families ruined by the spending of someone who was unmedicated and bipolar).

I could even potentially see there being a law enforcement issue of creating a panic or riot, exaggerated for example: "I'm going to take this money and throw it on the tracks at a train station and people can see how much risk they're willing to take to get it".

But "you have to give us an acceptable reason"? No. I am of comfortable but not exorbitant means (lower six digit salary), and my cash withdrawal limit, by default, is $15K/day. And the one time I asked for that to be raised temporarily, the only questions I got were for an additional piece of identification, and that they were able to call the contact numbers they had for me on my account to verify that it was me who picked up the call. Not "for what purpose, sir?"

Maybe it was a bank transfer.

your bank owns your money?