In terms of client hardware, I got those speeds using my Windows desktop setup. The desktop has an i5 12400 processor, 16GB RAM, multiple m.2 drives/HDDs, and a 10G NIC. I'm also using Wireguard. What's funny is that when I used Mullvad previously, I achieved gigabit upload speeds with an old laptop with Linux that only had an i5-43100U and a decent SATA SSD.
As for my network setup, everything is on a 10G connection – my ONT, router/firewall, and switch. I've set up a DIY Opnsense firewall/router with a 10G NIC. However, I'm currently limited to just a bit over gigabit speeds (1250 Download, 1050 Upload) since my ISP's plans go up to symmetrical gigabit speeds. Despite having the capability for symmetrical 10 Gigabit speeds using 10G EPON, they offer plans only up to gigabit speeds.
My internet is residential fiber from Spectrum, which is unusual as they typically provide service via Docsis over coax. Interestingly, I used over half a petabyte of data over a few months with their service and didn't hear anything from them. It's quite funny considering I was expecting some sort of notice for excessive data usage, even though they don't enforce data caps.