There’s not a huge amount you can do without drastically changing the voice.
To make the voice more intelligible through the pops and crackles, you could use the Pop Mute effect to lower some of those really big pops, and then apply some fairly brutal Equalization to bring out the voice and cut the rumble and hiss.
Here’s a before/after example:
This was the Equalization curve that I used:
The Pop Mute effect is available here: https://forum.audacityteam.org/t/new-plug-in-effect-popmute/17499/1