Need help with the Ethernet connection

Hey, first time posting here/installing macOS.

Let me start off by saying that my motherboard has no documentation whatsoever on the internet, believe me, I tried looking for it. It's an OEM motherboard put inside a prebuilt PC. It shows up on dxdiag as Pegatron IPXSB-H61, in case you want to put your Google-fu to the test.

Anyways, AIDA64 on Windows says the onboard Realtek LAN chip inside it is "RTL8139/810x", while DPCI Manager on macOS says it's "RTL8105E". I've tried out all available kexts, and found one that actually works; Mieze's RealtekRTL8100 kext.

Now here's the kicker: It works for a total of five seconds after boot. I can open up Google, Reddit, anything that's possible to open in those five long seconds. After that? No luck. The green dot next to Ethernet in Network settings turns to an orange one, and doesn't turn green till I restart the system.

Is there a way for me to fix the issue, or do I have to buy an Ethernet card?