Unless you want to deal with Fedora's release cycle, you're not going to push software through their repos. This isn't a Tailscale thing, this is a "just about everyone" thing.
>Something I don’t understand is if the client is open source, why is it not in the fedora repos? Why do I need to add a new repo to dnf?
Just because one group of people haven't done something doesn't mean it doesn't qualify. To show the exact opposite, look at OpenBSD. They have included Wireguard into their kernel.
Fedora not including Wireguard may be political, personal, or none-of-the-above. Maybe somebody hasn't offered to take on that task/responsibility.
I'm not sure if GP was referring to a wireguard package or a tailscale one. But to complete the picture, there's also a tailscale package in OpenBSD's repos.
Something I don’t understand is if the client is open source, why is it not in the fedora repos? Why do I need to add a new repo to dnf?