I would never brush or floss before, unless I had just eaten something awful within the last hour or so. I think it is best to stick with your normal routine. You give the hygienist a better look at how good or bad your cleaning is. They can easily tell what is recent and what has stuck to the teeth and requires scaling. Furthermore, you aren’t saving them any stink. The stuff that you need their help to clean out smells about 50 times worse than the things you just ate (just smell your floss compared to your breath after any meal). A quick rinse with water will get the worst out of their way, and even if you’re a sloppy eater the rest will take maybe 5 minutes at worst to remove.
I’ve been doing it for so many years across all devices and platforms that I actually get…confused for a second when one slips through. It is normally YouTube that slips through (they seem to be trying new things almost daily to get around any possible ad blocks), but sometimes it is from a major news web site or something. I actually have to look around for a second and then realize what has just happened.