The following issues were found when scanning project for PHP compatibility issues in preparation for upgrade to PHP version 7.4:
Warning in plugins/advanced-custom-fields-pro/includes/acf-field-functions.php: Since PHP 7.0, functions inspecting arguments, like func_get_args(), no longer report the original value as passed to a parameter, but will instead provide the current value. The parameter “$post_id” was used, and possibly changed (by reference), on line 569.
I don’t know about the rest of any errors, but I use ACF with php 7.4 all the time and there are no issues. The error you posted, the key phrase here is
The parameter “$post_id” was used, and possibly changed (by reference), on line 569.
Inspecting the code shows that this value was not passed by reference and is therefore not altered by the function.
But i am not facing any run time error. When we generate PHP 7.4 combability report of our master branch then this type of warning/issue generated. it will not create any effect on my website but we should solve that.