While resizing, or all the time, or at other times?
If it's not while resizing, then it's probably different to what this thread is about.
Excessive CPU usage in Opus is usually caused by 3rd party components that hook into the process, such as shell extensions. See here to troubleshoot that kind of issue:
Old thread, but similar issue.
I recently made a dual boot Win7/10 setup, and I noticed a significant decrease in display performance under Windows 10 (build 2004), especially when resizing listers containing files with Unicode (kanji) characters. The horizontal scroll is also stuttering -- it's running at 60 fps in Win7 but it seems cut in half in Win10. I disabled the old usual culprits like blending features (which I believe were fixed some time ago) to no avail.
Like the OP, I have no problem with other applications. This is not a deal-breaker, but it's rather annoying to have better performance under goold old Win7.
Ryzen 2600X (12 cores) + Vega 56 (Radeon driver 20.3.1) + Win 10 (build 2004) + DO 12.19
Maybe one of the recent updates of Win10 is causing this issue as reported by several sites. Don't know the exact Microsoft Knowledgebase article but if you google for this, I bet you will find some sources.
Anyway I don't know if this applies to your config...
Thanks for the tip, I'll do some research. I'm on the slow ring, but again I have to stress that Opus is the only app which seems to have that display (refresh, resize, scroll) performance issue. Even launching a new lister is visibly slower than under Win7.
Are you displaying the same kanji characters in the other apps which seemed to be involved in the slowdown?
That sounds like an issue with font rendering somewhere. If so then I'd expect similar characters to slow down at least some other software. (Not everything uses the same APIs to display text, so it might only affect some things and not others.)