It’s most likely watching Youtube with your VPN that’s broken then, not NewPipe. Youtube implemented Captchas for IPs that generate a lot of traffic/a lot of people are using. That’s how they are trying to kill frontends like invidious that proxy the requests. NewPipe by default uses your own IP so it doesn’t have that problem. If you use a VPN IP that a lot of others are using too, you’ll get that same problem though.
I’m not a fan of the xfce UX at all, and multi-monitor support still has a lot of issues (under Debian 12), but I am pretty sure having different refresh rates is possible