As far as I know, you can build a wall no more than 2 meters high. Next, you will either have to plant plants that will trail in height or pull on a mosquito net, which will slightly reduce visibility and create a shadow. So far, these are all possible legal options that you can implement. To calculate the number of materials and what can be created for the required height, https://www.heightcomparison.com can help you. You can also contact landscape designers who will be able to prepare proposals for you based on your request and area.