Question about Low-Data Mode

Hi everyone. Subject pretty much sums it up. A debate has been going on for some time now as to whether or not my neighbor across the hall and I have wi-fi issues. We have been sharing a wi-fi connection for a few years in order to split the cost. He has an iPad, an Android smartphone, and a smart TV which I think only utilizes wi-fi when connected to Netflix which he has had now for around 2 years. I have my Mac, iPhone, and an Amazon device which a tutor and I recently moved into my bedroom because we were re-arranging my apartment a bit. The A-person is connected to a power strip, so whenever I use that device I need to switch on the strip. My electric toothbrush is also connected to the power strip in there, but that's not the issue since the toothbrush itself is portable and can work on battery power. But it seems that whenever most or all the rest of these devices are connected and in use, our wi-fi slows down. This neighbor has been on a weekly video call with someone, and that is probably going to continue due to the pandemic. Here's my question. What is the actual purpose of Low-Data mode and Wi-Fi Assist on the iPhone? Some staff members here keep insisting beyond a shadow of a doubt that all this has nothing whatsoever to do with the connection up here. These staff members have told my parents and my neighbor's living family members the same thing. Tia for anyone's assistance, and sorry for the somewhat long-winded post.