I really liked the Tomato firmware for these things a while back... Been using OpnSense currently, with a dedicated AP mounted centrally in my home. It's a shame that the FCC rules have pretty much guaranteed that routers will only allow signed firmware updates, though the companies could do it differently. In the end, I miss the plethora of home hardware that can be consumer maintained and upgraded. I've avoided most "smart home" stuff for that reason.