Tailscale is an open-source VPN service without a central gateway service. This allows your reMarkable to connect to your other devices even when not connected by USB cable or on the same wifi network. See the documentation for more.
NB: these instructions have worked at least once, but have not been thoroughly vetted. As always, modifying your reMarkable is at your own risk.
reMarkable does not appear to have the tun kernel module available, which means reMarkable cannot use the VPN transparently. Other machines can connect to the reMarkable as normal, but for outgoing connections from the reMarkable will need to be configured to use the SOCKS Proxy.
tailscale and tailscaled under /usr/bin and /usr/sbin, respectively. (Or /opt/bin if using toltec.)/lib/systemd/system/tailscaled.service.[Unit] Description=Tailscale node agent Documentation=https://tailscale.com/kb/ Wants=network-pre.target After=network-pre.target [Service] ExecStartPre=/opt/bin/tailscaled --cleanup ExecStart=/opt/bin/tailscaled --state=/var/lib/tailscale/tailscaled.state --tun=userspace-networking --socks5-server=localhost:1055 --socket=/run/tailscale/tailscaled.sock ExecStopPost=/opt/bin/tailscaled --cleanup Restart=on-failure RuntimeDirectory=tailscale RuntimeDirectoryMode=0755 StateDirectory=tailscale StateDirectoryMode=0700 CacheDirectory=tailscale CacheDirectoryMode=0750 Type=notify [Install] WantedBy=multi-user.target