I usually swear by Stéphane Pigeon’s mynoise.net. These are soundscapes, but presented without the usual spammy clutter and low-quality adware. These are multilayered noises of high quality. They cover everything you’d think of: purely artificial white- and gray noise; complex mechanical soundscapes; natural ones with wind, fire, rain, waves; chants and drones and throat-singing and instrumental plonking; abstract synthesized musical patterns, ASMR; role-playing backdrops and in-utero noise; binaural beats and neuromodulators. You can mix and match soundscapes here, tweak them, even animate them.
I have ADD and work in an open office. My co-workers rarely bother with moderating their tone or affect. This page has kept me functional and on-track on quite a few days when that would otherwise be a struggle.