Flatpak finally works in Linux Mint 19.3, unfortunately without theme support
There have been serious problems with the flatpak version of Geary before on Mint 19, but since version 3.36.2, the flatpak works flawlessly. Thanks for your hard work. Unfortunately, it doesn't respect the Mint-Y theme, it displays in Adwaita instead. It would be wonderful if this were fixed.
PS For me Geary is the best mail client on Linux. Beautiful. Modern. Minimalist. Well-designed. You can really rely on it. It's really useful.