GTK 4.0

If GTK 2 apps are sufficiently important to you, I'm sure your help would be appreciated. The people packaging GTK 2 apps as Flatpak apps don't *have* to be their upstream maintainers, any more than the people packaging GTK 2 apps for Debian have to be their upstream maintainers.

It's also entirely possible to build Flatpak-style runtimes from Debian packages: https://salsa.debian.org/smcv/flatdeb can do this, and is used to build the Debian-10-based Steam Runtime v2 (which is not currently distributed as a Flatpak runtime itself, but is "the right shape" to be used as one). GTK 2 is available in Debian 10 and will be in Debian 11. I don't currently have enough bandwidth to be trying to build production-quality Debian runtimes alongside my other responsibilities, or to set up, sysadmin and fund a suitable hosting platform (CDN?) for distributing them, but someone could.