Start with your cable modem or whatever router your ISP uses to connect to the Net. Reset it. Then reset any Wi-Fi hotspots or routers you have inside your house, in a sequence starting with those directly connected to your ISP router/modem. Then reset your computers.

That will cause each device in-turn to refresh its network identity with the next device up the line. In doing so it will also load new routing tables.

One other consideration -- is your home firewall set to automatically establish a VPN to your office? If so, you might be routing all Internet through your office network and they might have filtered Defender as a "non-business" site.