its got nothing to do w/ your connection or the i browser use. Somewhere between you and I here in Australia and the UK a security script has been installed and is corrupting our cookie profile. The advice all over the net advises cleaning cache blah, blah, but as soon as you log in with your username here. The cookie crumbles, or gets scrambled, as it were. My question to you and not saying it is a remedy (nor the issue as I havent either) but wondering have u up upgraded to windows 11 yet ? I suspect that might help, but not certain.
Your options are to browse in Privacy and Incognito mode - dont log in, you can then browse at regular speed.
When you do want to communicate and log in, click the padlock at the beginning of the URL, that helps for a bit by removing your registered cookies at this site, but will eventually it slow down again.