How can I quickly edit a selected frequency range in Audacity (for example, reduce its volume, delete, fade it)?
If you know what frequencies you want to affect, Effects → EQ and Filters -Filter Curve EQ.
If you want to experiment, the Graphic EQ is easier to play with. There are also other filters and a couple more under Effects → Legacy → Classic Filters.
Fading filters is not so easy… . You’d have to make duplicate tracks with and without filters and crossfade. (It may not work “smoothly”.)
There is also Spectral Editing.
No. I wanted something like iZotope RX. It’s clear that Audacity still has room for improvement))