.7z being there just discredits the entire process. The underlying compression algorithm is a free-hand one and can be anything[0], or contain bugs and exploits[1]. Personally I use only zstd with .7z which is 'non-standard' by the official (Russian) release.
reply[0]: https://7-zip.org/7z.html
[1]: CVE-2025-0411
I love using zstd, it's so fast to decompress. I especially like that the JavaScript decoder is 8kb and still really fast. Though the 25kb wasm decoders are about twice as fast.
replyWhat are the advantages or reasons to use zstd in a 7z container versus just .zst?
I love zstd as the next guy and I do use zstd solo for the most part. I had a talk on it few years back too (incl. using the lib directly from Java, massively decreasing log storage, and so on).
replyWhy use it w/ 7-zip though. 7-zip archives multiple files/directories and supports encryption. It has the UI too.. On Windows there is NanaZip that's available in the microsoft store which has been graced by corporate for user-install (unlike zstd that effectively needs WSL), and most folks won't be able to use the command line tool.
Of course using tar with zstd is always an option if you are on linux.