is there an eraser tool in mac preview?

Preview is not a PDF Editor, and prior to Preview in macOS 11.1, you cannot "erase" any original text created in the PDF. With Preview in Big Sur (11.1), one can actually apply a redact annotation over selected text, and that text is permanently removed from the original PDF with only the following remaining where the original text was located:

For Catalina and earlier, if you want to "erase" text in a PDF, you would have to purchase a PDF Editor from the Mac App Store (PDFpen, PDF Expert, etc.). Applying an opaque rectangle over text neither erases it, nor prevents it from being searched, or revealed by other tools.

Not that I recall but one can Overwrite a text with Black-Lines to basically " Redacted ". In more Full Feature PDF Apps one can Erase text