How to minimize pdf file size on mac without losing quality?

You can use Preview.

Open the PDF in Preview and choose File > Export > Select Quartz Filter > Reduce File Size

Compare the exported file with the original before sending it. If the result looks soft or the file is still too large, use a PDF compressor that gives you control over the compression level.

PDFgear for Mac is a good free option for this. 

Open the PDF with PDFgear. Go to the Tools tab > Compress PDF > Choose a level:

Low for documents where image and scan quality are most important.

Medium for the best general balance between file size and readability.

High only when the attachment limit is strict and a noticeably smaller file matters more than image detail.

For a report or presentation, I would normally try Medium first, then inspect charts, logos, and small print before deciding whether to compress further. For a scanned document, Low is usually the safer starting point because every page may be stored as a large image.

Also, there is no compression method that guarantees a dramatically smaller PDF with literally zero change in quality. The goal is to remove unnecessary data or reduce images only enough that the difference is not noticeable for the way the document will be viewed or printed.