Internet and WiFi work fine with other devices. My Macbook is the only one that is experiencing slow/intermittent connectivity. Only in the house, not elsewhere.
1) Airdrop goes and scans for peers periodically and borks wifi. Try ifconfig awdl0 down. See https://news.ycombinator.com/item?id=31706283
2) Try separating your 2.4 and 5GHz networks and locking the mac to the 5GHz. I've got the same SSID for 2.4 and 5GHz and I've seen my MBP cling to my crappy 2.4GHz network because it has a stronger signal, but much wonkier performance. There is apparently no way to just disable the 2.4GHz radio on a mac!
3) My partner was having a problem where she'd loose wifi connectivity on her mbp every hour. It turns out that some security protocol on wifi does a re-key every N minutes. This is supposed to be seamless, but my partner's ISP provided wifi AP did something that made the mac loose connectivity on re-key until she disabled and re-enabled wifi. I proved this was the problem by changing the re-key interval on the router. We "solved" this by replacing her router. This had the advantage of getting her much cleaner spectrum, since the ISP provided routers don't use DFS, so all the APs around her were clogging the same few 5GHz channels. Between fixing the re-key issue and the DFS, her wifi got much, much better.
Also, in addition to speedtest / fast.com, etc, I'd suggest using https://packetlosstest.com/. Seeing spikes of latency over 1-2 seconds brings home problems like crowded channels, or the airdrop scanning.
Happy hunting!
Sounds silly but I found out that my macbook pro 2020 when wakes up from sleep with external monitor connected it will have no internet or very slow connection, until I unplug the monitor and replug it again