Alpine edge testing apps are in postmarketOS edge. So yeah, not all of them make it to stable, but quite a few do:
For software listed on https://linuxphoneapps.org/ the count is as follows: Alpine 3.19: 160 Alpine edge: 198
(Source: https://linuxphoneapps.org/packaged-in/)
The difference should be mostly the apps that have not made it beyond testing, yet.
Please note that you can also try installing testing apps on stable by apk add PKGNAME --repository=http://dl-cdn.alpinelinux.org/alpine/edge/testing
, or, maybe as more safe way of doing this, use distrobox, install alpine:latest in it, and changing /etc/apk/repositories/
to make it edge instead of 3.19.
You can also try to build some software that's not packaged by coming up with your own APKBUILDs, I did so a while ago on https://framagit.org/linmobapps/apkbuilds, maybe the notes I left there can be helpful to you.
Regarding Wikis: They always get stale, so clarifications and additions are surely welcome!
I was referring to "Flatpak [...] is currently only working as expected on x86_64" is ... if not false, then far too easy to misunderstand. Flatpak works just as well on aarch64 for (at least) hundreds of apps. The software that's not available on, e.g., flathub for aarch64 (but is available for x86_64) in most cases is not available (in compiled form) for aarch64 at all — because it is proprietary with vendors not caring about aarch64, or ... just is electron-based ;-}.
It's not Flatpak, it's the entire aarch64 software ecosystem that's lacking here. Stating "Linux on aarch64 has less available software than x86_64, which is especially so for proprietary software" would have been a far better statement.