句子总体是个“主系表”结构：

the target（主语） was （系动词）what he called coordinated inauthentic behavior, fake accounts where people deliberately hid their identities to mislead others.（表语）

下面重点分析表语：

表语是由一个从句充当：what he called coordinated inauthentic behavior, fake accounts where people deliberately hid their identities to mislead others.

1. 按现代英语术语，what 叫做“融合性关系代词” （传统语法叫做：复合连接代词），它本身既充当了先行词，又是关系代词，身兼两职。等于：the thing(s) that。

2. what 在其引导的从句中，作了called 宾语，后面的coordinated inauthentic behavior, fake accounts 是“同位关系”，共同作宾语补足语（结构是：call + 宾语 + 宾补）。又如：

This is what we call Beijing Opera.  这句是我们所说的京剧。

That is what we call anxiety.  那就是我们所谓的焦虑。

3. where 引导定语从句，修饰accounts，而to mislead others 是从句的目的状语。