Depends

Most phones can be accessed by forensic software. The more secure phones are protected as long as they've just been restarted but before they're unlocked for the first time.

Some phones, like an up-to-date GrapheneOS on a supported Pixel, may resist forensic imaging after first unlocking but the information is in memory so there could potentially be zero days or other exotic methods of obtaining the data.

A duress wipe lets you know 100% that the data is not accessible.