Not really. As soon as you have a path from global internet into your home network, all bets are off and you’re now in charge of securing all of that against the entire world.
That said, if this is a regular old HTTP service, I believe Cloudflare Tunnels offer a way to put an authentication mechanism in front. This can work if, just like with Tailscale, you have a limited known set of users but the difference is that those users don’t to have to install and use a VPN client to access your service but rather authenticate using an “external” HTTP service through their browser. Again, I do not believe this works for services accessed through APIs and certainly not ones using custom protocols.
I can’t stress enough that getting those remote users to use Tailscale is probably the best and easiest solution.