In my home I've had to get TP-Link to give me dedicated firmware for my Mesh Network which puts each of my 4 XE75 routers on different channels to cut down on the 2.4Ghz traffic congestion, have an old M5 in the mix which is for my backyard in in the base of my Swim Spa to help with backyard cameras. I also have TP -Link plugs on some of my Google Home Speakers that will only turn on if I want them on or turn on automatically when motion is detected.
I'm currently on vacation and there are 80 devices connected to my network, 9 of which are Nest Cameras (2 are Nest Hub Max's which are only on when no one is home) 4 of my Google nest mini's are off currently as we are away as well as Google Home Max. Multiple smart speakers as well as Google TV's which are always transmitting packets seem to be the biggest issues with congestion, which you can control if not using be having them turned off with a smart plug to reduce network congestion.
I've resorted to limiting the wifi devices I buy and going with thread or ZigBee with new purchases, mainly Aqara products which I set up my DIY security system since Nest Secure ended. I haven't added up my network devices in a while but I would be well over 130 and have no issues now with gaming play Call of Duty or PUBG on the Xbox. Definitely as recommended in the article rum ethernet to any device you can. Also with my Mesh Network I've set up ethernet backhaul to also cut down on traffic.
Even though TP-Link and other say they can handle 150+ devices it would depend on what type of devices you connect as my network gets wonky after I see 100+ on the Wi-Fi network due to the 9 camera's, 9 smart speakers, 4 Chromecast (2 of which are google TV's) and then just the pure number of other smart devices. Packet traffic seems to be my biggest issue which I can only resolve by taking devices offline when not in use, although being on different channels helped considerably as well as another change they made (which I can't recall as it was 9 months ago and my brain is in vacation mode)