I setup a PC as a router and used an internal PCI / M2 card as an AP in the past but, to get WIFI 6 you don't have any options currently to do this. You can host an AP with a card though for AC speeds. I do have a WIFI 6 capable Intel AX411 running in AP mode but, the bandwidth is limited to ~200mbps through it. With the AC card I was using though I could get close to my full bandwidth up to about 1gbps. Using an AP though connected to the PC I can hit 1.5gbps using an AX411 client with DCT enabled which bonds both 2.4/5 bands into a single pipe for increased bandwidth.
If you want to run internal AP you'll need a QCA / MTK / BCM based card and use linux with hostapd. There are a couple of options with WIFI 6 out there and I tested the most recent MTK7921 and it wasn't all that stable for speeds and required disabling WIFI 6. There's a QCA based card I was looking at but, the vendor was out of stock and couldn't get my hands on it so I dropped the idea and stuck with my actual AP instead since WIFI 7 is around the corner and double the speed possibilities.
As for the whole DIY router it works better than relying on the buggy junk you get off the shelf and pay too much for. If you're thinking about using the 4790K system in your signature it would provide enough horsepower to get it done. It should be capable of providing enough speed if you're using a VPN on it as well. The PC option gets rid of the headaches with VPN's by allowing line speed encryption using wireguad compared to a router in a box.
