When I migrated from a 2015 27" iMac to a new Studio Mac and Display all of the sudden my Internet became abysmally slow. I called my provider and they could find nothing wrong on their end. I tried adjusting settings across the board and could find nothing. I finally saw an unrelated post where someone mentioned as a side note turning off the Private Relay beta to solve a similar issue. I tried it and it turned out to be the culprit. When it is on Safari slows to a crawl and my common pages such as banking sites time out before they load. When it is off things return to normal.