I am not with Laminar Research; just a flight simmer. As I live downunder I have no connections with any of the retailers mentioned below and or the products mentioned..
X-Plane is very resource hungry. Don't think about a Mac system as you will spend a lot more cash than what you will with a windows based Mac system to get a top of the range system. A desktop will also allow you to upgrade your components as time goes by whereas I am of the opinion that is not possible with a Mac. Your system will need good cooling as there is a lot of heat generated by the processor and graphics card. A non Mac will allow you to install additional units if required.
You need a good processor that can be overclocked (speed enhanced) so you need either an Intel 7th generation or 8th generation i7 processor that has in its designation the letter "K" eg 7700K or 8700K.
For top of the range go for a NVidia graphics card rather than an AMD card. Certainly with X-Plane 10 NVidia was giving a better performance than AMD. The at the top of the range is a GTX 1080 or at the top is the GTX 1080ti . The brand selected, generally Gigabyte Geforce, depends on the specs of the card. A GTX 1070 card will give a reasonable performance. I understand there is a new 1100 and or 1200 series cards about to be released.
You haven't indicated where you live. If you live in the UK contact a PC reseller called Wired2Fire whose web site can be found at https://www.wired2fire.co.uk/gaming-pc
If you live in the USA contact Michael Brown at XForcePC. This site can be found at https://xforcepc.com/flight-simulation-systems Once you connect with this site click on the flight simulation tab and you will get a choice of flight sim computers or flight sim systems. Have a look at both. This company is recommended by Laminar Research (X-PLane) as the supplier of PCs in the USA capable of running X-Plane. XForcePC will dabble in other flight sim packages upon request.
Before you spend your money have a look at the Youtube videos created by Michael. There is a lot of good or useful information made available for the "newby" The link can be found at https://www.youtube.com/user/col2mab/videos I have this link listed as a preferred site and I look at it quite regularly.
Good luck and welcome to X-Plane.