IMO it's really unfortunate that Monocypher doesn't implement a high-level CSPRNG API. I appreciate that it goes against the design goal of being entirely dependency-free, but getting random number generation wrong is such an easy foot-gun in my view, and it's already my least favourite part of libsodium (its most obvious "competitor") that the AEAD constructs don't generate a random nonce for you.

Edit: Also, not sure why the author chose to use Argon2i over Argon2id as the PBKDF for Monocypher, my perception was that the id variant should be used unless you have a reason not to. Would be interested to hear other opinions on this.