Using a reputable paid VPN is the most common method, but as you said, some are slow. For a stable connection, you need a service that regularly updates its IP addresses to avoid detection. A good starting point is to learn how to unblock Instagram safely. A detailed comparison of methods, including using specialized browsers, can be found in this guide
https://gologin.com/blog/how-to-unblock-instagram-in-your-country/ . The goal is to have consistently unblocked Instagram access without compromising your account's security.