How to Set a Default Printer (Windows and Mac)

Windows

Go to Settings → Bluetooth & devices → Printers & scanners. Click the printer you want as default, then select Set as default. If you don't see that option, check whether "Let Windows manage my default printer" is turned on near the top of the Printers & scanners page — this setting automatically switches the default to whichever printer you used most recently, which can feel like the default keeps "changing itself" if you regularly use more than one. Turn it off if you want a fixed default that doesn't shift automatically.

macOS

Go to System Settings → Printers & Scanners. Near the bottom, find the Default printer dropdown and select your preferred printer from the list. Mac also offers a "Last Printer Used" option in that same dropdown, which behaves similarly to Windows' auto-switching — if jobs seem to be going to different printers unexpectedly, check whether this is selected instead of a fixed printer.

If the wrong destination keeps getting selected anyway

Even with the correct default set, some applications remember the last-used printer per-document or per-app rather than respecting the system-wide default. If this happens consistently in one specific application, check that app's own print settings or preferences for a separate default-printer option that might be overriding the system setting.

Removing a "PDF" or "Fax" printer from being the default

Virtual printer entries like "Microsoft Print to PDF" or "Fax" appear in the same printer list as real physical printers, and can accidentally end up set as default. Follow the same steps above and simply select your actual printer instead — there's no need to remove the virtual entries, just make sure they're not the one marked as default.