Do any countries have any flight restrictions that might not be widly known?

Sorry but that's a huge question with way to many answers.  Any country in particular?

Each country would most likely have different laws. Which country/countries are you looking into?

Once you know where you are going a good starting point is the DJI Fly Safe page where you find information on all countries: https://www.dji.com/flysafe?site=brandsite&from=homepage
In addition a Google search will help and you can ask forum members here who either live in the country concerned or have been flying there.