2.4 ghz wifi and microwaves are darn close in frequencies (actually overlap) and that is a very common problem. Given how weak wifi signals are (in the mili watt range) an the 1000+ watts a microwave puts out, wifi safe microwaves are not realistic because the shielding would triple the price. Switch to 5 ghz and no more problems. Almost all routers unless it is 15 years old can do 5 ghz. If your laptop or desktop is also ancient, a $10 usb 5 ghz unobtrusive little wifi unit will solve your problems.
Turn off beam forming and MIMO. They are teats on a boar unless your client expressly supports them and the implicit beam forming just doesnt work.
If for some crazy reason your wifi router doesnt do 5 ghz, something cheap like this works as a fine router. https://www.amazon.com/ASUS-AC1750-WiFi-Router-RT-AC65/dp/B091D71M6P or this https://www.amazon.com/TP-Link-AC1750-Smart-WiFi-Router/dp/B079JD7F7G
If it just your computer that does not do 5 ghz, something like this adds it https://www.amazon.com/TP-Link-Mini-Wireless-Supports-10-9-10-14/dp/B07PB1X4CN and something like this adds it with a lot more range because of the antenna https://www.amazon.com/wireless-USB-WiFi-Adapter-PC/dp/B07P5PRK7J
Thanks for the feedback.
I’ve since moved house and my office is now where my router is - so I switched to a wired connection.
I get no interference from my microwave oven on 2.4GHz.
I did try putting some water in the microwave and running it while my laptop was pinging the default gateway via a 2.4GHz wifi connection.
No packet loss at all.
Then I started pulling on the door at the top edge away from the hinge.
I was able to make it start dropping packets by pulling on the door with just a little force. Not enough to make it pop open, but just enough to distort it slightly so it compromises the shielding and allows 2.4GHz RF leakage from the microwave.
The harder I pulled, the more packet loss I saw.
As soon as I let go, the packet loss stopped.
Conclusion: A properly functioning microwave oven causes no interference to 2.4GHz wifi.
However, even the slightest warpage of a microwave oven door is enough to compromise the shield.
Therefore, if your microwave oven is causing 2.4GHz wifi interference, there is a good chance that something is wrong with it. Replace or repair as needed to remedy the problem.