Great question. I'm wondering the same thing. I also built a PC in 2017 and installed Windows 10 on it. It initially had a 7s boot time following bios startup. Several updates later, the boot time is now close to a minute and app startup times are noticeably slower as well. I've always been very careful about what software I install on it. I've done all of the standard troubleshooting, but so far it hasn't gotten bad enough to warrant a fresh install.
Thanks, that was the first thing I tried. I didn't want to go into great detail about my troubleshooting efforts because I don't think it's quite relevant to the overall discussion.
