Can I repair a stone step?

I have a 1911 property with a stone? back door step which is worn and either crumbled or cracked.

A few years back a plasterer did a repair and think skimmed it, but needs doing again.

I had a Google around and Toupret exterior masonry repair filler had good reviews, as well as U-can repair steps concrete repair from B&Q.

I can do most things and am happy to give this a go.

I think the step needs an angle adding or building up so the water runs away also.

Any advice or thoughts much appreciated.

Pictures Added

Here is the step from inside and outside.

Also photos of windowsills, also needing work to help with type of stone.