iStats returns an error on ARM processors (M1)
The error mach-o, but wrong architecture indicates that the iStats Ruby gem expects another chip architecture. I assume you're using a new M1 chip?
Looks like the iStats gem does not yet support M1 (see #107).
Prepending the command with arch -arm64 in the index.jsx seems to resolve the issue but iStats does not work 100%. Fan and battery stats seem to work but others return no values or are missing.
I was able to resolve this issue by installing Ruby 2.7 from Homebrew and updating the path to Ruby to ensure the homebrew version preceeded the Apple version. The homebrew version of Ruby is not a universal binary. Its specific to aarm which resolves this issue.
However, once past this issue, you'll likely run into others. Specifically, battery and fan info is incomplete.

Thanks for that workaround @stevespringett.
Unfortunately istats does not support M1 (yet) and my C and SMC knowledge are inexistent.