How are you on virus scanners? Do you use them and are they current and active or on at least a weekly schedule?
In my neighborhood we are certainly having demand issues due to Covid and everyone being home and so many people working from home or otherwise heavier than normal load. Always had a period around 4-7 pm when people got home where I could tell the difference from my normal morning usage. As a gamer, I am watching my computer and connectivity performance. Browsing at home doesn't usually impact me too much -- except trying to get into my Comcast email and I blame that purely on them.
Have you checked to see what processes are running in the background? You can bring up Task Manager in Windows applications.
A lot of programs now have what I consider intrusive operations and don't necessarily close off your system just by hitting the X button which is the convention. With my gaming software, Twitch which is now owned by Amazon wishes to "stay resident" as we said in the old days. I've said before that I'm getting to the tinfoil conspiracy level theorist about my beliefs of privacy and the internet which has been now developed by commercial enterprises solely as a means to get through that privacy and try to sell me things that I have no wish nor desire nor need to buy....