The explainshell output is actually largely wrong here. For historical reasons, GNU ps has two completely different sets of flags depending on whether you use a dash (ps -abcd) or not (ps abcd). The man page documents both sets, but explainshell is getting confused and showing a mix of dash versions and non-dash versions. For example, it shows the documentation for '-f' ("full-format listing"), but it should be showing the documentation for 'f' ("ASCII art process hierarchy (forest)").

(I considered filing a bug report, but there is one already: https://github.com/idank/explainshell/issues/214)