BearSSL is probably the best documented cryptographic library I've come across. It also has a unique feature of being able to compile the resultant objects to only include what you need and nothing else making it great for embedded, specifically anemic devices.

Unfortunately it kind of halted development many years ago and hasn't really progressed since.

Perhaps since it was a pre-AI project, it might make sense to continue it with heavy use of LLMs, but with every LOC being human reviewed.