My iMac from end of 2015 with Monterey
After my many phone calls with Apple support (and let me say that I'm pleased with the time they took), the problem wasn't solved untill I came across the link below. I configured my network(s) as 2.4 and a 5Ghz. So the original network was named xxxxxx and the second one xxxxxx5 for the 5Ghz one.
I connected my mac to the xxxxxx5 and the wifi speed was up 10-fold.
So, what the cause of the problem is I don't know but for my this was the solution.
https://www.macworld.com/article/675313/how-to-switch-to-5ghz-on-a-mac.html
Most negative thing about it all was that someone from the helpdesk let me know the possibility that end of 2022 it just might be the last update for the systems produced before 2016. I would detest that from Apple.