joslmetz wrote:Difficult to spot the boundary between XAMPP and Joomla in this case.
its not a question of "boundary", its still a Joomla issue. Joomla requires PHP5 and then you cannot use a Xampp version which comes with PHP7. But the issue remains a Joomla issue.
Think of software, which requires Windows10 for example and it fails to run on Windows XP (for example). That is of course an issue of that software, it is not a Windows issue. Same thing here, first of all you have to establish a runtime environment, which fits to the needs of Joomla. Xampp does not mind, which Joomla version you will try to install. Just vice verse, Joomla requires a certain Xampp version. A Joomla support forum (as well as an installation description) should give you the information, which PHP versions are supported. But a Xampp forum cannot give you any information, which Joomla releases are supported. Therefore, you should ask in Joomla forum. Joomla needs a Server environment like Xampp, but Xampp does not need Joomla.