Already reads as such, though I've tried that code snippet too:
PostUp = iptables -A FORWARD -i %i -j ACCEPT; iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE; iptables -A FORWARD -o %i -j ACCEPT
PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE; iptables -D FORWARD -o %i -j ACCEPT
Like I said, everyone keeps saying Wireguard is dead simple to set up, but the comments are full of editing configuration files, priv/pub key pairs, etc. I've helped administer OpenVPN servers for a decade now (and take no pride in it), and yet all these errors that keep coming up in Wireguard configuration for me on a main Linux distro + Windows 10 client seem pretty odd for something that's supposedly so easy to use.
Someone just come out with a wizard/package installer that actually works reasonably well (like OpenVPN has already) and then it might be "easy" to install. For OpenVPN I run an apt install command, run a wizard, SFTP into the box, transfer out the .ovpn file, import it into whatever client devices I need, and it works. Wireguard is at least 10 times tougher than that, even if it worked, which it currently does not.