Tried max performance settings. No difference.
When cursor over the icon and the animations starts,
Desktop with R5-5600x+GTX1060(6GB), 1~2% CPU usage;
on my Laptop with i5-8300H+GTX1050, 10~12% CPU usage.
Is that normal to consume that much on a i5 8th-gen CPU?

However, I don't think it's normal to lag even in the settings window when switching tabs.

Well, to start with the Ryzen has 6 cores while the i5 only has 4 cores, both having hyper-threading (so double the cores). This means on the Ryzen maxing out a single core would show up as 100% / 12 cores = 8%, while on the i5 a single core maxed out would show as 12.5% (100% / 8 cores).

To find out why this is so you can read a short explanation I posted regarding the CPU Meter module HERE.

Still doesn't explain the massive 10% difference which must be due to other factors. Perhaps your laptop only uses the GTX1050 in performance mode, using the built-in iGPU otherwise - with Nexus being graphics intensive, the fact that the iGPU is using slower system RAM for graphics instead of fast VRAM could explain the difference. Then there are other factors such as memory speed (animation graphics are stored in RAM), CPU speed (the faster and more efficient the CPU is the faster it can render), etc...

Anyway, here is a link to Optimizing Nexus for speed and memory usage that might prove an interesting read to you.

As for your screenshot, I have no idea what is going on in there, but you seem to be using some third party Windows customization software you forgot to mention based on those extra titlebar buttons?

Anyway, you can always try disabling the UI animation in Preferences -> General tab -> More Options button -> Disable User Interface Animation.

Problem solved with a restart. Still, Thanks.