bash does not honor ~/.inputrc
after examining the issue under linux, i realized that the issue is not macos specific.
searching the internet harder, i found the solution

you can't get this feature in BASH at present because this feature hasn't been built yet into vi or emacs mode. As I commented above completion-ignore-case only applies to completion, not to isearch

~10 years after the accepted answer, it seems that it is still the case.
references:

Find out corresponding escape sequence for a given key combo
Search for a previous command with the prefix I just typed
In bash, how do I bind a function key to a command?