Having been caught out recently when a web site I launched displayed perfectly on IE, Firefox, Chrome and Safari on Windows but was corrupted when viewed using Safari on the Mac
These sites may help:
Browsera
Browsershots
See tutorial here: https://www.wikigain.com/install-macos-high-sierra-virtualbox-windows/
You will get the latest Safari.
You don't need to pay for those online services!!!
Use these vbox settings to increase resolution and memory, but it is still very laggy and slow:
cd "C:\Program Files\Oracle\VirtualBox\"
VBoxManage setextradata "macOS" VBoxInternal2/EfiGraphicsResolution 1920x1080
VBoxManage modifyvm "macOS" --vram 256
https://turbo.net/ offers a browser sandbox in which containerised virtual machines run browser sessions for you. I tried it with Safari on my Windows development machine and it seems to work very well.
https://appetize.io/demo?device=iphone8&scale=75&orientation=portrait&osVersion=13.3 60 seconds is enought for test. Isn't need to register account to.
Meanwhile, MacOS High Sierra can be run in VirtualBox (on a PC) for Free. It's not really fast but it works for general browser testing.
How to setup see here: https://www.howtogeek.com/289594/how-to-install-macos-sierra-in-virtualbox-on-windows-10/
I'm using this for a while now and it works quite well
Unfortunately you cannot run MacOS X on anything but a genuine Mac.
MacOS X Server however can be run in VMWare. A stopgap solution would be to install it inside a VM. But you should be aware that MacOS X Server and MacOS X are not exactly the same, and your testing is not going to be exactly what the user has. Not to mention the $499 price tag.
Simplest way is to buy yourself a cheap mac mini or a laptop with a broken screen used on ebay, plug it onto your network and access it via VNC to do your testing.