Crossing the Atlantic is done in true. Presumably other oceans too.
Maybe it is now, with all the Space Age gear you have, but when I navigated the Atlantic using a chart, Douglas protractor, Dalton "computer" ( before the word was hijacked by Bill Gates ) ruler and sextant I would plot a "fix" then measure the true track and distance to the next reporting point or required track change, (the word "waypoint" hadn't been invented,) then apply the mean Variation between where we were and where we were going to, to give what was actually a mean Magnetic heading to steer to the pilots.
The only time we measured True and steered True was over the Polar region.
Only the Navigator had some idea of where they were at any given time, ( Flt. engineers had to be able to do sums, co-pilots had to be able to write and the Captain had to know someone who could read ) and even the Navigator only really knew where they had been, i.e. at his last "fix", 'cos plotting position lines from whatever source, Astro, Loran, Consol, NDB or whatever, took time to get down on paper by which time the aircraft had moved on, so immediate present position was always an estimate. VOR/DME was the nearest one could get to exact "present position" I guess, but there were none of those over the Atlantic ( or any Ocean, and few deserts )