I did have to specify
--stable to pickup the update. Inkdrop launched fine after a successful download.
I’m now seeing what looks to be GTK3 UI (launched from Preferences > Backup location) but it’s using a light theme (Inkdrop GTK seems to be ignoring my OS prefs). The same appears to be true of the application menu below the application title.
By comparison, GitKraken, Slack and VS Code all seem to respect the OS preferences for a dark GTK theme (all Electron apps as I’m sure you’re aware) but I’m unsure if these are defaults for those apps or whether they truly are respecting the OS prefs for a dark GTK theme.