I would like to suggest that you buy some 1/4 round in the size to cover the gap and install that.
This gap is like an expansion joint in the concrete, it lets the wood flooring expand and contract with the building and the weather.
Sealing it up might not allow this process and the flooring could buckle up.
Put the 1/4 round down and stain or paint it and this will cover the gaps and look nice also.
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