I think I got my Inatek card for about $30-40 a few years ago. I have no reason to believe it wouldn't work in in Windows today and I just confirmed that it works fine in macOS.
All Coffee Lake systems are limited to 40 PCI lanes, 16 from the CPU and 24 from the Z370 chipset. The 16 from the CPU is intended for GPU use and many motherboards with more than one x16 slot will make the first two drop to x8 if both slots are used. From everything that I've read, this is plenty for all current generation GPUs and will not affect performance.
The remaining 24 PCI lanes are used differently by all the different motherboard manufacturers. Built-in features such as ethernet, USB3.1, audio, etc will all use up some of those lanes. Some times motherboards with lots of PCI-e slots will have slots/features switched. A pretty common example would be cases where usage of an M.2 slot would disable two SATA ports as is shown in your attached photo.
This is why I never saw much logic to getting full sized ATX motherboard in Coffee Lake and older "consumer" level chipsets such as Z170, Z370, etc. There simply isn't enough lanes for all the extra PCI-e slots, at least without compromise. This also explains why on my Strix Z370-G Gaming motherboard, there are two x16 and two x1 slots rather than two x16 slots and one x4 slot. There just wasn't enough lanes.
Based on your attached image, the following two x1 slots should work for your card. If you use the other x1 slot, you may need to do something in BIOS to disable SATA #1 to enable that port.
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