I had a similar problem. Large archive files, quick random access was paramount. I considered SquashFS, but rejected it due to poor tooling on Windows, and I wa

I had a similar problem. Large archive files, quick random access was paramount. I considered SquashFS, but rejected it due to poor tooling on Windows, and I wanted my thing to be cross-platform. The format also seemed like something I'd need to spend some time understanding. Surprisingly, ZIP came to my rescue. It's surprisingly flexible, and includes support for Unix attributes and modern compression. In comparison to tar.xz, it was strictly superior in every way. ISO is also a good format with broad support, with many platforms now supporting mounting the contents using the built-in OS features. The only downside I could find is lack of compression, but there are supposedly format extensions that can help with that.