Not an apartment, but in a neighborhood of small lots of many duplexes and townhouses.
Before it used to be about 1 SSID per family and it was relatively possible to get channel 1, 6, or 11 to yourself or with an overlapping signal being very weak and far away, but now with everyone rocking mesh units and guest access and Comcast public access, the number of SSIDs in the 2.4ghz range have tripled and I'm pretty much surrounded by strong signals on all channels.
I don't have too many HomeKit accessories, but the ones I have aren't an issue. Indeed, the ones I have use either the AppleTV as their hub via bluetooth (Schlage) or have their own hub (Philips Hue). Nest thermostats and Arlo Q cameras both support 5ghz wifi, but aren't HomeKit.
My only remaining 2.4ghz devices are my older Apple Watch, the MyQ garage door opener, my older Brother printer. Also technically Sonos uses 2.4ghz, but with SonosNet it's sort of a separate thing anyway.