nvim-shell-completions VS bash-completion

nvim-shell-completions/nvim.completor.bash

Look into the bash-completion project. I'm not sure about "brief descriptions", though: It's possible with bash's programmable completion functionality, but I don't think bash-completion even tries to do that.

What exactly do you mean. bash by itself only has very limited autocompletion. With tools like this and some manual work you can make it better.

Even though there is a library of completion scripts like scop/bash-completion, it only includes common commands. For some commands that are not commonly used, we have to write completion scripts by hand.

BTW, it's not needed to assign $cur for the word containing the current cursor position, or prev=${COMP_WORDS[COMP_CWORD-1]}; it's already in bash-completion lib, and can be reused with _comp_initialize (renamed from _init_completion):

bash-completion - is a collection of command line command completions for the Bash shell, collection of helper functions to assist in creating new completions, and set of facilities for loading completions automatically on demand, as well as installing them.

Tab completion doesn't come from the "cryptsetup" program itself, it comes from a third-party project (https://github.com/scop/bash-completion)

Neither the terminal emulator (konsole in your case) nor Linux are the relevant piece of software. What matters is the shell and whether there are completion scripts for those commands. On my system (Debian with bash) completion works for both sudo and flatpak. The completions for sudo are provided by https://github.com/scop/bash-completion, the ones for flatpak are part of the flatpak package.

Also take a look into https://github.com/scop/bash-completion which might be available as a package on your distro, named most likely bash-completion.