I went to Adobe's website, and couldn't find a non-subscription version to just buy, so I actually contacted customer support about it, and they said "nope, you have to pay for a subscription".
I could have of course sailed the high seas, but I opted to just buy a copy of Toonboom Harmony, which is fairly different than Flash but close enough and still offers perpetual licenses (and shockingly works pretty well with Wine/Proton on Linux).