There are some good tips in this thread below. Within the Firewalla iOS app, I use the Wi-Fi Test to validate my speeds from the phone to the Firewalla before checking ISP speed connections. My biggest issue on the 5 GHz band was interference previously, by performing a scan in the controller I was able to manually set 5 GHz to a channel that wasn’t being used and I disabled meshing in the AP settings since both of mine are wired. Even with just one AP, I was getting 300-900 Mb/s in the Firewalla test throughout my house setting a channel for 5 GHz manually. This is on an iPhone 15 Pro Max while trying 20/80 MHz and 20/160 MHz for the 2.4/5 GHz bandwidths. I also WFH and have similar Apple devices to what you listed.