Deprecated: The each() function is deprecated.

[bondash]

A New Collabtive 3.1 using PHP 7.2.0 is throwing the error "Deprecated: The each() function is deprecated. This message will be suppressed on further calls in C:\xampp\htdocs\collabtive\vendor\smarty\smarty\libs\sysplugins\smarty_internal_compilebase.php on line 78"
It is safe to downgrade PHP to 7.1.9 or should I go back to an especific version?

[Eva]

You can either continue to use PHP 7.2 or downgrade to 7.1.0 - both should be fine.

The information about the deprecation is not an error, but just a warning. The "each()" function will only be turned off in PHP 8, as you can read here:
https://wiki.php.net/rfc/deprecations_php_7_2

You could change your Collabtive production website's error reporting, so it only shows errors, but not the less serious stuff like notices and warnings.