TL;DR: I don’t daily drive (Free)BSD because it doesn’t work with some hardware and software that I use.
I’m not an expert in the BSD’s. But I’ve tried to daily drive FreeBSD a couple of times and can speak to it for myself from that viewpoint. Most recent attempt was about a year ago.
The issues I had:
Poor WiFi support. I understand that wireless driver support is iffy and even if it does work, it has poor speeds. I tried this on my laptop and could not get WiFi to work. There was a workaround in passing wireless card through to an alpine Linux guest VM and connecting there then creating a bridge. I did get this to work, but I found it impractical.
Games (via Wine/Proton) aren’t really an option. I understand you can install steam via a Linux compatibility layer and it’s somewhat functional with workarounds. I did not try this.
Those were dealbreakers for me. But the desktop experience itself was good. I ran KDE, and it felt the same to me. if I was running it on a wired machine that wasn’t used for gaming, I think I’d be happy to use it.
Almost any distro will work for pretty much all of that. Only potentially limiting thing I see there I don’t think that the Mullvad VPN client is generally available within distro repositories. Their site says it has clients available for Ubuntu, Debian, and Fedora. So perhaps pick from one of those?
For the steam link question, I know if I have a game running on my desktop it presents me the option to stream to my laptop (both Linux machines). I assume this is the same functionality. I don’t use it so can’t speak to how well it works.
Edit: It occurs to me this comment lacks a recommendation. Within the three listed supported distros for Mullvad, I think I’d recommend Fedora for you. Been some years since I used it last but I remember the installer being fairly robust and intuitive while still easy to use, and a pretty rock solid system once it’s up and running.