Of course, this is a kill switch, but that's usually detectable if the attacker is sophisticated enough. Plus, they can always backup the disk before.

Plausible deniability lets you pretend you do not have incriminating data, but it's tricky to use in the first place: https://gitlab.com/cryptsetup/cryptsetup/-/wikis/FrequentlyA...

Travelling with an empty disk seems like a more appropriate option. Dm-verity could probably be used to check that there has been no tampering.