I suggested to FP support to add the ability to remap the Assistant button. In other words, a double click could then disable ANC. And a single click then cycles between Ambient mode and ANC.
A better solution is for the device to turn on in the mode it turned off in. The device has to have non-volatile storage in order for it to save bluetooth pairings. A couple of bytes of that storage for this issue would make the device much friendlier.
Why not both solutions? Easy switching and an option to save the setting. I personally prefer a default mode when turning the device on and then have the ability to effortlessly switch.