Sometimes you might get odd network behaviour, such as unreliable connections, failure to connect to web sites, email behaving oddly, failure to print on networked printers, etc. This might be caused by some special or unnecessary network settings on your Mac. Here's how to disable these.
Note: These instructions are for modern versions of the OS, such as Sonoma or later. If you use an older OS, these settings might be in a different place, or missing entirely. Just change what you have access to, especially IPv6.
Go to the Apple menu, then "System Settings". Choose "Wifi" from the "View" menu. Turn "Private Wifi address" OFF. Turn "Low data mode" OFF. Turn "Limit IP address tracking" OFF. Click on the "TCP/IP" tab (on left). For "Configure IPv6" choose "Link-Local only". Click on the "Proxies" tab (on left). Turn all the options OFF.