Youtube works too slow on PC, only via wired connection

Hi all,

I've just set up a KPN home ethernet connection and noticed some issues when using a wired connection. Specifically, certain services—especially Google-related ones—are extremely slow:

• Google Maps: Takes nearly a minute to load every time I move the map.

• YouTube: Unwatchable at resolutions above 480p—constantly buffering.

• Twitch (I know it's not a Google service): Streams don't load at all.

I've tested this on Firefox, Chrome, and Edge with the same results. I'm not using any ad blockers or extensions that might interfere.
I've also tried resetting the router, but it didn't improve the situation.

Strangely, when I switch to Wi-Fi, these issues mostly disappear—though the overall connection is slower than wired, everything works more smoothly.

Has anyone experienced something similar, or can offer advice on what might be causing this?

Thanks in advance for any help!