I have enjoyed a soft murmur on days where I need to focus. A soft murmur is a neat little website where you can build your own soundscape. You can even subscribe to access the full sound library. I have used this site on off for at least a decade.

The free version is great already btw. For years I used singing bowl, birds, rain and waves as my soundscape. After I became a subscriber I got into crickets and frogs xD

As far as I know, this is an initiative by one guy so if you decide to subscribe, the money goes to him. He has a bio on the site that describes the story behind the website and his mission with it, but I don't remember it super well. Haven't used it since October because my life has been a hectic mess haha.