Is the equinox absolutely true east everywhere? I've read that only only in the equinoxes do you get to see the sun rise in the exact east regardless where you might happen to be. However I think this is not absolutely true everywhere, but only in the equator, and in the south the Sun will rise just a tiny bit to the north, but this tiny bit to the north is negligible due to how far the Sun is from Earth. If this reasoning is correct, when would the 'true' equinox be for any country in the south? Can you provide an example and how you did it, please?
The celestial equator's plane intersects the horizon due east and due west, no matter where you are on Earth (except at the poles where the horizon is the celestial equator).

Those that have the sunrise at the exact time of the equinox will see the sun rise in the east (90º). For the rest, it will be too late, the sun will have made the crossing, and it could be something like 90.00001º or 89.99999º, although it will still be perceived as due east.

The last equinox was March 20th, 03:50 (UTC). At that moment the sun was rising very close to Maputo, Mozambique (table), so everybody on that meridian saw the sun rise in the east, exactly at 90º.