The recommended way of obtaining cabal is via ghcup.
For installation/upgrade instructions using a previous version of cabal-install see here.
To manually download binaries for many architectures browse the subdirectories of https://downloads.haskell.org/~cabal.
Report bugs here or to the cabal-devel mailing list.
You can get the development version of the code here.
Stable Releases are numbered a.b.c.d, where b is even. Unstable snapshots between releases are numbered a.b.c.d, where b is odd. Changes for c and d are minor.
For example, 2.1.x.x is the development version leading up to the stable release 2.2.x.x.