For the terminology used in linguistic papers, it is quite confusing. It seems that [complement] and [adjunct] are a pair of concepts that are often distinguished from each other. However, sometimes, the other two terminologies, [modifier] and [argument] make the situation more complex. Does complement mean argument and adjunct mean modifier? Can I understand it in this way?
Unfortunately, many technical terms in linguistics are ambiguous, because they are used differently in different traditions. "Complement" and "adjunct" are a case in point. It is probably always the case that these two are seen as opposites, but the definition can vary. I would assume that "argument" and "modifier" are less ambiguous, but who knows. With argument and modifier, you rather stress the semantic function. "Complement" and "adjunct" are used in generative grammar as purely syntactic notions, namely positions in the syntactic structure. You may then wonder whether there are unifiorm ways of interpreting them, that's a tough question, there is probably a correlation in that complements often have the function of an argument and adjuncts (even more often) as a modifier. But modifiers can occur as "specifiers" or even as structural complements at least in some theories.
But that's the interpretation of the terms in generative syntax. As far as I can see, there is also a more traditional understanding of these terms that identifies them more or less with the semantic function or argument or modifier.
I once researched precisely this question when I wrote the articles "Komplement (Syntax)" and "Adjunkt (Syntax)" for the German wikipedia. The result which you find there is that complement and adjunct are presented as ambiguous terms, with the variants traced back to different sources. I see that, in the English wikipedia, the article "adjunct" has a different approach and seems to emphasise the correlation between the grammatical and the semantic side of the notion.
The terminology of linguistics is a mess, everyone admits that...