尝试取消选中设置 - 项目下的排除构建目录复选框设置 - Maven - 导入。

Try to uncheck the Exclude build directory checkbox under Settings - Project Settings - Maven - Importing.

来自IDEA帮助的说明：

Description from IDEA help:

选中此复选框可从项目中排除构建目录。如果您想加快项目的导入过程，这可能很有用。如果清除此复选框，则每次导入项目时，IntelliJ IDEA都会对构建目录中的文件编制索引，这可能需要额外的时间。

Select this check box to exclude a build directory from the project. This might be useful, if you want to speed up the project's importing process . If this check box is cleared, IntelliJ IDEA will index files in the build directory every time you import a project which might take additional time.