De-Esser and De-Clicker are designed for mouth noise problems.
https://forum.audacityteam.org/t/updated-de-clicker-and-new-de-esser-for-speech/34283/1
You can start a new track under your existing one (Tracks > Add New) and put a “processed” Room Tone on that track. Loop it until it comes out the right length. It will play at the same time as your dialog and will automatically mix when you File > Export.
You’re still going to get gating artifacts, but not as loud.
Koz