PC Engines ALIX platform is very robust, combined with open source routers from OpenWRT or opnsense https://www.pcengines.ch/alix.htm

https://opnsense.org/

https://openwrt.org/

any flavor of linux imaginable can also be loaded onto the ALIX platform, if you want more granular control (router solicitations, nat subnetting, etc...)

2.4 and 5ghz can be added with mini pci cards or with inexpensive openWRT devices connected via traditional cat6, or even USB dongles if your priority for 2.4 is low.