Aether refers to some historical ideas (which evolved over time), and though the word isn’t in use anymore the current model of fields has similarities (ofc in many ways very different). Have just been reading some of the history of this (Einstein plays a big role), it’s very interesting, thank you! :) You might be interested in this discussion https://news.ycombinator.com/item?id=27942970

Way over my head unfortunately

Wilczek points out that field theories are aether theories — as is relativity.

“Aether just means this one particular historical model!” is branding more than reality; and hides the fact that modern theories also describe an everywhere substrate of which particles are localized excitations and gravity is localized warping.

Air is aether.

Air is not required for an E field to exist or propagate.

EM fields propagate just fine through vacuum, they are mediated by photons.