Your guide looks really complicated and I'm not sure why all of those steps were required for you to get online.
You could have probably just bought a simple IOGEAR adapter like this one: https://www.amazon.com/IOGEAR-Ethernet-2-WiFi-Universal-Wireless-GWU637/dp/B018YPWORE
Just plug it into your PC to configure which Wi-Fi network it connects to or use the WPS button then, after configuring the adapter, you just plug in a network cable from the Dreamcast to the adapter. (Remembering to plug the adapter into the wall or a surge protector for power.)
That should be it.
There is! You can find it here https://cdromance.com/psp/phantasy-star-portable-2-infinity-jpn/
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(Sorry if I am not allowed to link)
I'm in the UK as well, is it this https://www.amazon.co.uk/Phantasy-Online-Songs-Ragol-Odyssey/dp/B00006IIEU? It's in stock same as the cd in the other link i supplied earlier, just second hand.
If you after brand new, your going to pay even more for it, if you can even find it.
I'm not testing anything right now, and I haven't used my DS4 in a bit. But I had no problems using my DS4 on Eph with Win10.
This is the more active branch: https://github.com/Ryochan7/DS4Windows
It also appears I have "Hide DS4 Controller" enabled in settings.
I heard that Crossover (a commercial version of Wine) can run 32-bit Windows applications on Catalina and beyond. I haven’t tried it myself so I can’t say if it’s true or not.
Depending on if you’re willing to spend some money so you don’t have to go the bootcamp way, it might be worth trying their trial!