A circular saw does not have a square cut as the blade is … well circular. The deepest part of the cut is in the center of the blade. To completely cut one board you would have to partially cut the next. Modern floors have sub floors that they are nailed to, while some very old floors were nailed directly to the floor joists.

It is possible to remove individual planks, however it will require a number of techniques and tools for a neat job. It is not something to try if you can’t handle a circular saw like a pattern maker uses sizzors and have a good mechanical skill with tools and wood. Both of these things are not implied in your question.

You may additionally require a hammer, vise grips, a punch, a sawzaw, a cats paw, a flat bar, a very sharp chisel (and possibly not just the edge a new chisel comes with.) If you manage to get what you want out, to replace a new board eithor a tongue or a groove will have to be cut off for it to fit into the middle of the floor. You will probably need a table saw for this. You will therefore probably also need some surface nailing that can be covered up or plugged.
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I have Braz cherry…I could darken it and the finish is Bona Naturale, which is a "natural look" finish, not satin.