TL;DR: It certainly is possible from a geosynchronous orbit, an altitude of 35786 km. It is also possible from a very high altitude weather balloon.
A key issue is that the terminator is not a line. Thanks to the Earth's atmosphere, the terminator is instead a band that is about 1000 km across that gradually transitions from sunlit to dark. At most latitudes sunlight notably starts to decrease at least 10 minutes before sunset, but one can continue with outdoor activities for a half hour or more after sunset. (The reverse is true for sunrise.) That 40 minute period or longer time span corresponds to a very wide band. Even an SR-71 could barely have seen that ~1000 km wide band that transitioned from sunlit to dark.
In addition to barely being high enough, another issue with an SR-71 was that they moved so fast. Something that flies even higher than did an SR-71 but flies much, much slower than an SR-71 is needed. That would be a high altitude weather balloon. A high altitude weather balloon (30 km or higher) could see both the bright and bright sides of that 1000 km band, and it could see that band slowly moving.
Even higher up (much higher up), that widish band doesn't look at that wide from the perspective of a geostationary satellite. Now it does looks a bit like a line. Just as is the case with a geostationary high altitude weather balloon, a geostationary satellite would be able to see the terminator (now a line rather than a band) move over the more or less stationary Earth.