Isn't 2.4GHz too congested already, esp considering a lot of wifi-connected devices still work at that range? I typically go the other way around to avoid congestion.
This is Europe where we have concrete or masonry walls and good insulation, I see maybe 2 other APs in the worst days in the apartment. On the good days I have no other APs.
I saw about 50 in maybe 10 years old apartment building, once the new ISP in the block started giving people routers with wifi enabled by default
I don't know about other areas but any apartment buildings post like 1990s are just absolute junk when it comes to separation. Before then it was just concrete or structural brick and now somehow it's often 'fireproof magicboard'.
I recall being surprised that 2.4 GHz was completely unusable in an upper west side apartment. <56k throughput and >1000 ms latency.