Look, what you have is probably fine, but you just have to accept that you now have this page open to the world and you are relying on Synology to be on top of their security and you to be up-to-date.

I use Cloudflare tunnels myself for Plex and the like (separate VLAN), but I keep my local Network and all portals only available via a VPN.

Pretty sure they all use Webkit so doesnt really matter (on iOS). I use FF for personal and Edge for work.

All my VMs run Ubuntu server and the actual metal server itself runs Ubuntu.