Capitalism did not exist in Adam Smith's time and that kind of pre-capitalism he did criticize, saying that the division of labour is very productive, but tends to make workers stupid because the tasks are exceedingly simple.

Marx basically based his entire theory on that observation: if the tendency of capitalism is to dumb down formerly artisanal work to a very simple assembly line, then it treats every worker as an unskilled worker and thus can exploit them.

Smith did not see this far, he was merely worried that the dumbing down of tasks will make workers stupid and thus not good at e.g. being workers.

Smith could not criticize capitalism because it did not exist yet, but did see the core problem in that pre-capitalism already: the dumbing down of tasks.