Safari will not support Canva

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MacBook Air 13″, macOS 10.13

Software update may not be available for the macOS installed on your Mac.

Consider upgrading to a later version if compatible with your system.

Update: A later version of the currently installed software. Learn about macOS Big Sur updates, for example.

Upgrade: A major new version, often with new system requirements. Each macOS upgrade has a unique name, such as macOS Big Sur

 Learn more about installing the latest macOS upgrade. Some old versions of macOS are also available.

Published Date: June 11, 2021

    https://support.apple.com/en-us/HT201541

Here is some information that may help you to understand what is happening. As noted, your version of Safari is not compatible with that web site. However, Safari is installed as part of the operating system and it normally it cannot be individually upgraded. It is usually updated when the computer's operating system is updated or upgraded. This is not an unusual situation. The reason is that web site engineers write their software to work with specific browsers and specific versions of them. If you are unable to upgrade your OS you can use another browser that does work such as Firefox or Chrome. They can be individually updated as needed. Finally, even if you are able to upgrade Safari, there is no guarantee that it will be compatible.