Version of Windows? Is this a new problem or has it always been this way? How many other devices are on your network and is any of them having speed problems too? Have you rebooted the router lately? Are all your drivers up-to-date? Have you checked the Link Speed between your PC's Ethernet and the router? That's the speed PC and router talk to each other, not your internet down/upload speed. You should be getting a Link Speed of 1000 Mbps, assuming your router supports 1000 Mbps Ethernet Can you try a direct connection to the router, without using the house's wiring, with a CAT6 cable?  Keep in mind that performance decreases with increasing length of the cable. Have you tried disabling SmartByte software which manages internet connections? Dell installed SmartByte on the Inspiron 3670. You don't need SmartByte at all and It can slow down network connections. EDIT: Can we assume the house wiring ends at an Ethernet jack on the wall, and you use a short cable between the wall jack and the PC? If that's correct, what's the rating of this cable, and have you tried a different cable to the wall jack, using a CAT5 or CAT6 cable?  Or at least unplugged and replugged the existing cable at both ends?
My Dell 3670 Inspiron has a Realtek PClE GbE PCI card and the computer is wired directly to my Eero Mesh router via a Cat5e cable.  I am getting my paid for 200 Mbps download, 100 Mbps upload at the router when checked with my Eero app.  I cannot get more than 100 Mbps on the download speed on my 3670 at the computer when checked with Ookla.  In my network properties for my Win10 OS, the 3670 it says 100 Mbps and even if I change the settings, it reverts back to the 100 Mbps setting.  If I switch over to wifi on the 3670, I can at times get more than 100 Mbps on wireless, but I want to use the direct ethernet cable connection for stability when streaming through Zoom and other online streaming meetings.  On this device I don't want to use wireless. Could this problem be solved by installing a faster network adaptor card?  Is that possible?  I think my existing network adaptor is on the mother board and don't know if that would be a conflict.  What is troubling to me is that my existing Realtek PClE GbE PCI card should be rated for gigabyte speed, but it appears to be throttling me at 100 Mbps. The Cat5e cables were installed when the house was built 14 years ago and replacing the Cat5e with an upgraded cable is not a possibility.   Thank you in advance for any assistance you could provide.
Dell Inspiron 3670 throttled at 100 Mbps