Richard Osman has spoken about books being optioned - it was really interesting. He said it’s very common for books to be optioned by production companies, as they want to make sure they have a large body of available works on their slates for possible future production (essentially, it’s a story bank). But, in Richard’s estimate, only 1% of those options will ever actually end up being produced.
The authors get paid a nominal fee to grant the company an option for a period of time, from 1-5 years normally. They don’t get paid a large fee unless and until the production actually starts. (Richard would know all about this as he was approached by Stephen Spielberg to option the Thursday Murder Club just before it was published. He said he said yes to the deal not expecting that it would ever be turned into a movie, but because he thought it would great to help with marketing the book when it was published (“as optioned by Stephen Spielberg” etc). He was paid around £5k I think he said. Of course, the book was a huge success, and a movie really is being made - he’s in the lucky 1%).
So, Netflix taking out an option on Meet Me At the Lake is no indication that anything will happen in relation to that.