I just downloaded Opera GX yesterday, and I haven't changed any settings, but certain websites time out. This includes Google, Youtube and Twitter. Other sites load perfectly fine, including DuckDuckGo.
I have disabled my firewall and ad blocker, and I am not using any proxy services. Each of the sites listed above works on Firefox. I am using Mac OS Catalina 10.15.5 on the most recent version of Opera GX (released today). This problem was still happening before the update.