Following this thread, I have enabled Software flow offloading and I'm getting nearly 800Mbps / 100Mbps without SQM.
Hope it will help somehow, since wife issues with the internet still happens. Seems like streaming Netflix / Playing Xbox while I'm on a Zoom call as well preventing her from getting access - i.e. she have total lost of connection. When she do have a connection she get around 180Mbps/90Mbps but with BufferBloat C on her Macbook Pro 13 2020. I still can't pin the main issue...
I have checked on the same location as she is, with my Lenovo T14 Gen1 Ubuntu 20.04 and I get around 300Mbps / 100Mbps with BufferBloat B.
I'm starting to think the issue is with the Mac NIC...