Solution:
Turn on graphics acceleration in the settings. If it's already on and/or doesn't help, then I have no idea.

@leocg Sorry, I am a little late, thanks.

Opera GX's CPU usage is ~40% when Speed Dial tab is open. It started doing this recently, no idea why, but looks like other people have the same problem. Disabling mods helped getting it down to around 20%, but it's still low FPS when on the Speed Dial tab.
Using Shift + Esc, I found out that the two processes heavily using CPU is "GPU Process" and one of the "Renderer" processes.
Here are some screenshots:

Also, these two mod slots have some kind of warning sign:

Using the CPU limiter doesn't really help, in fact it seems like it makes it even worse.

That's all I could find, thanks for any help.

@dddddddddddx I have the exact same problem, any fixes?

How the heck do I delete it now?