The most polished Glacier backup/restore mechanism I know -- because I helped build it -- is through rustic <https://rustic.cli.rs/docs/commands/init/cold_storage.html>. It has native support for backing up to Glacier (because writing to Glacier is identical to writing to regular S3), and it supports external "warmup" programs to support cold storage of your choice, with Glacier having an existing warmup program you can use.

I am a solo developer of a niche CLI application. The use-case is backing up your computer data to S3 Glacier (cold storage) and later restoring from it.

I took two actions to distribute my app.

First, I automatically build static binaries for Windows, macOS, and Linux: https://gitlab.com/philipmw/warmup-s3-archives/-/releases/v1... . This part is fully within my control, and I believe these binaries fully cover the potential audience. This works well because my app is just one binary, so I am not worrying about distributing assets or other complications. If you like this, adopt my `.gitlab-ci.yml`.

Second, I am already a Nixpkgs contributor, and I added my package to Nixpkgs. Nixpkgs is niche in its own way (as you point out too), but it makes it trivial to adopt my app if you're already using Nixpkgs. Given that my app's intended audience is very tech-savvy, Nixpkgs is probably a good fit here.