It depends on how much should be open source (wifi generally involves a lot of blobs), and how much the router should do more than just route, but a good starting point should be OpenWRT on supported hardware.

I tend to separate the router and access points. Well working wifi hardware has traditionally been hard to find on consumer pricepoints, so I've used Ubiquiti thoughout. They're not open source at all, but neither are most network cards and wifi adapters so I consider them appliances. That way the router can be simple and separate.

It's spendy, but my OpenBSD router is from here https://protectli.com/ and they do support a wifi card and the Ralink driver works in OpenBSD.

I prefer to run wire up wireless APs though.

Have you checked out the Turris Omina? It's built to run OpenWRT.

https://www.turris.com/en/omnia/overview/

Do you mean even the Hardware are open sourced or any router that is capable of running OpenWRT?

There are plenty of options for OpenWRT.

Running OpenBSD may better fit your description of "dream".

You can get an 802.11ac router that supports openWRT, but I haven't found any yet that support 802.11ax. They're all broadcom chips. Fuck broadcom.

PC engines APU have some coreboot board for router. You can run any OS you wanted on it.