How can I route all traffic through a VPN with my TP-Link Archer A6 V4?

Hey everyone,
I’ve got a TP-Link Archer A6 V4 and I only have one Ethernet port in my room. I want all my network traffic to go through a VPN. I tried installing OpenWRT, but the V4 version isn’t supported.

I also have a Raspberry Pi 3 B+ I could use, but it only has one Ethernet port. I want to make sure the part between my PC and router stays wired so I don’t lose my 1 Gbps speed. I also have a USB-to-Ethernet adapter, though I’m worried it might slow things down.

I’m not super experienced with networking, so I might be saying something wrong. What do you all recommend I do? What should I buy (budget-friendly)? Thanks in advance!

Also please let me know if any more information is needed I'll be happy to provide.