malware affecting web browsing?

I have an Early 2015 13" MacBook Pro running Catalina 10.15.5. Over the last few weeks, web browsing in both Chrome and Safari has become severely limited - in both browsers, sites often will refuse to load (Safari will return an immediate "Safari can't open the page" error, as it did when trying to load this site), or if they do load, will load basic HTML only. If I refresh enough, eventually the site will load, but often without images.

I've run virus/malware scans using Avast, Trend Micro, and ClamXAV and have gotten nothing. Would appreciate any help or suggestions.