So what replacements for Audacity exist?
Not much afaik. There's Mhwaveedit which still uses GTK2 I believe. Or
Ocenaudio which is not open source.
Neither are as full featured as Audacity, nor appear to have development
in the last 3 years or so.
gnusound [1] and rezound [2] springs to mind but I'm sure any of those
are actively developed anymore.
[1]