OpenWrt is a great piece of software(firmware) to prevent ISPs selling your browsing data to the advertisers. Although by now most ISPs are probably doing packet inspection.
It's easy to customize, I have a script to notify me when a new device connects to my router[1] and I also have a script to notify me when someone logins into my router[2].
Earlier I used to connect my openwrt router directly to the ISP's switch but now a days they've started to force their 'AI powered' router which is centrally managed. I now have to usee OpenWrt to defend against the ISP's router first and then the broader public network.
[1] https://abishekmuthian.com/openwrt-new-devices-connection-al...