Hi @BRhind29,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Your floorboards appear to be laminate flooring, which is made of MDF with a timber-look veneer.
In this situation, your best option is to use a coloured wood filler, such as this Timbermate Pine Wood Filler, to fill the gap.
Apply the filler to the gap using a Pro Renovator 38mm Plastic Scraper, allow it to dry, then give it a light sand with some 180 Grit Sandpaper, being careful not to scratch up the surrounding surface. If you are careful, you should be able to avoid doing so, but taping things off with some painter's tape is an easy way to protect the surrounding area.
The filler alone will not replicate the texture and grain of the surface, so you could use a utility knife to make some light cuts in the filler to mimic the texture and grain of the timber. Just remember to wear long protective clothing and gloves when working with knives.
You can then use an oil such as this Feast Watson Scandinavian Oil to help seal and protect the wood filler.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
