Today (10/15/2021) was a slow day on the internet. And by that I mean websites failed to load for me, or took a long time to load. I hit several "temporarily unavailable" on websites I frequent. It was either a big internet hacking day. Or, it was because I'm taking a cybersecurity course, in university, and I'm being hacked by intelligence agencies for suspicious behavior. I also had a slowdown when I took a previous cybersecurity class on Udemy. But, that could have been a big hacking day too.
Have you updated to Windows 11? It apparently has all sorts of issues. If not, then your ISP is probably throttling you in an attempt to get you to sign up for a more expensive tier of service.
Yes I did upgrade to Windows 11. But the slowness also happened on my phone in a different location while I was trying to reach the websites that were down.