It's a Mixte frame bike dating from the 70s or early 80s probably. And it looks to be in very good nick. Google "Motobecane Mixte" and you might get more info.
I don't know how much it's worth, £100 ... £200 maybe? I don't think it's a hidden gem worth zillions, even though it appears to be in excellent condition for its age. Really the best thing to do is to search
ebay or wherever for similar bikes. I believe prices may be high at the moment due to the pandemic knock-on effect.
Or - if it's the right size - just ride it.
Or - and this would be a shame but you could consider it - research and identify each component, then see what the individual components are fetching. There's a chance you might make more that way. But I don't think these are top end fancy retro components so that route probably wouldn't be worth the effort.
More likely to appeal to someone for nostalgia reasons than practicality reasons. Stem mounted friction shift gear levers aren't the height of fashion these days.