Hi TTTPTP,
Thank you for posting in the Microsoft community. We are happy to assist.
Based on the information you have shared with us; I understand you have a concern on previewing PDF from Outlook on the web in safari browser on mac. while testing from my side I was able to preview the PDF file sent on for the outlook. To fully understand the scenario you are experiencing, I would like to ask the following questions to narrow down the situation and work toward the resolution.
May I know if the downloaded file is opening the browser?
Based on the information you have share with us, it seems like there is a problem with the PDF viewer in the browser. Could you try to open any online pdf file to see if the file can be opened in the safari browser
when the pdf is open of preview it open is in a pop window, you can verify if there is popup windows are allowed in the browser. Go to Safari >> settings and allow pop-ups for Outlook
Remove Unnecessary Safari Extensions: Sometimes, extensions can cause conflicts. Try disabling any unnecessary extensions and see if that helps
Clear Outlook's Cache in Safari: Clearing the cache can resolve many browser-related issues. You can do this from Safari's settings
Please note that my initial response may not address your current situation immediately. However, with your help and more detailed information, we can work together to find a direction specific to your current situation.
I look forward to your next update. Thank you so much for your precious time. stay safe and healthy.