Do the basement and office have coax available? If so, MoCA might work for you. Pass the LAN traffic over MoCA into a switch in the basement.
Dumb question, but you have an Ethernet from the Eero going to the MoCA adapter near the modem, correct?
I've seen 5-6 Asus Zephyrus laptops refuse to connect at anything other than 100Mbps, even after turning off the auto-neg and setting it to 1G, they would still connect to the switch at 100M.
This has all been within the last 6 months, I wonder if they released a broken driver for whatever NIC they're using.
It knows the IP address associated with your modem and won't allow access outside of that IP address.
If you're using a VPN, that will cause problems.
Right? "Is this a camera?". Then proceeds to upload a video taken with a RAZR V3.