Its a PC running Linux as Operating System. Linux is a free Operating System, developed by a huge community, the base for many other developments (i.e. Apache, MySQL, PHP) and the most stable Operating System. The Xampp VM is an export of a Xampp Linux installation, running in a Virtual Machine. But it runs under MacOS with all the hassles of MacOS and Apple.
Apple simply lies when telling you, that everything is running smoothly just out of the box. You actually currently learn this the hard way. It does not work simply out of the box.
Linux comes in very many "distributions", for a beginner i highly recommend either Ubuntu Linux or Linux Mint. You can get free ISO images on the corresponding sites. Or simply proceed to
https://distrowatch.com/, you will find all of the distributions there.