You’d like to understand the various options you can use when starting bash, but bash --help is not helping you.

In addition to bash--help, try bash -c "help set" and bash-c help, or just helpset and help if you are already running in a bash shell.

bash sometimes has several different ways to set the same option, and this is an example of that. You can set options on startup (for example, bash -x), then later turn the same option off interactively using set+x.