Had the same issue. I have a VM at a hoster which proxies requests to my nextcloud server at home. Both the VM and my server on my home network are connected via tailscale. I've been using the VM for other stuff as well and happened to have it anyways, I didn't get one just for this purpose
TSG doesn't really support integrations like that. There are unofficial workarounds, but they're prone to break. Adding an API is on their roadmap, but might be a long time in the future