This already exists: in "Trip options", you can toggle between "Best route", "Fewer transfers", and "Less walking", as well as allow/block "Ride services" like Uber as a transport option.
How well these options work is another question, but "Fewer transfers" does seem to allow more walking. And of course you can straight up ask for walking directions instead.
Was about to write the same - those options do exist already.
It works quite well in my experience.
Although quality may depend on how well a specific city mapped out. Melbourne for example have options for accessibility (City consuls pays for mapping accessibility scores\options and I guess those details help to plan in maps and just generally a good city benchmark).
Preferred and connecting modes works well too - one can specify if ride service or drive is not an option or bus is meh. One thing I wish to have there is 2-3 presets of these options so I can quickly switch between combinations of - "get there fast", "get on specific time", "get with my most comfortable preferences". It's all there, just switching it every time is a bit of annoying.
How well these options work is another question, but "Fewer transfers" does seem to allow more walking. And of course you can straight up ask for walking directions instead.