Like why should I put time into learning this instead of rootless podman? Aside from this secret management thing it sounds like same feature set
Many container platforms are available, but Apptainer is focused on:
Verifiable reproducibility and security, using cryptographic signatures, an immutable container image format, and in-memory decryption.
Integration over isolation by default. Easily make use of GPUs, high speed networks, parallel filesystems on a cluster or server by default.
Mobility of compute. The single file SIF container format is easy to transport and share.
A simple, effective security model. You are the same user inside a container as outside, and cannot gain additional privilege on the host system by default. Read more about Security in Apptainer.