If you cannot change the microwave, consider trying a different wifi channel. I once had a 2012 Panasonic microwave that killed 802.11g channels 7 and 14 but not channel 0.
I am not too bothered about it. I only use it every other day for about 3 minutes to heat up some porridge. I keep on meaning to buy a new Microwave, I bought it in ASDA 15 years ago for £30 and it just keeps on working.