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For example, this feature will not be available on Ubuntu 18.04.
This feature requires Curl version 7.62 or later, and will not be available on older Debian/Ubuntu versions that do not bundle a Curl version later than 7.62.
Curl extension supports DNS over HTTPS (DoH) since PHP 8.1. However, the installation guide below does not include AVIF image support. GD extension supports AVIF image format from PHP 8.1 if the extension is compiled with AVIF image support. Extension and Dependency Changes in PHP 8.1 For a complete list of changes in PHP 8.1, see What's new and changed in PHP 8.1. PHP 8.1 brings several new features, improvements, and functionality that are marked deprecated. However, Ondřej Surý continues to make PHP versions available as a Debian/Ubuntu software repository, and PHP 8.1 packages are now available. None of the current Ubuntu or Debian software repositories offer PHP 8.1 in their default software repositories. Installing PHP 8.1 on a new system, or upgrading an existing PHP setup to PHP 8.1 is made easy on Ubuntu and Debian-based systems with the help of pre-compiled binaries.
PHP 8.1 is now released with new features, improvements, and deprecated functionality.