So I have jellyfin deployed to my kubernetes home lab, router port forwarded to the ingress controller (essentially a reverse proxy) on the cluster. So exposed to the internet. Everything on it has authentication, either built in to the application or using an oauth proxy. All applications also have valid SSL configurations thanks to the reverse proxy. I also use cloudflare DNS with their proxy enabled to access it and have firewall rules to drop traffic that hits port 80/443 that doesn't originate from those cloudflare proxy ips (required some scripting to automate). It drops a lot of traffic every day. I have other secuirty measures in place as well, but those are the big ones.
So yeah, if you expose your router to the internet, its gonna get pinged a lot by bots and someone might try to get in. Using a VPN is a very simple way to do this securely without exposing yourself and I'd suggest going that route unless you know what you're doing.