nimble install https://github.com/adokitkat/**bignum**
This was supplied by @lscrd in Aug 2023 on the forum.
Recently this did not work, but the following did:
nimble install https://github.com/adokitkat/bignum
which installs bignum 1.0.5
Note that --mm:arc and --mm:orc now work.
nimble install bignum
on nim 2.0.2 installs 1.0.4, not 1.0.5
I stepped on similar problem recently.
As soon as I figured out the reason, I switched my project to atlas.