Tailscale binding to only eth0 — how do others do this on DietPi?

Hi all,
I’m running DietPi with Tailscale and I want to force Tailscale traffic to go only through eth0 (not over other interfaces). I’ve tried systemd overrides with --bind=<eth0 IPv4> but it keeps failing to start.

Has anyone successfully restricted Tailscale to a specific interface on DietPi? What approach did you use — systemd bind, firewall rules (iptables/nftables), or something else?

Details:
eth0 IP: 192.168.178.28

Thanks in advance!