

Hmmm… there’s a few different things going on here.
As others have already said you don’t need a cert if you’re just messing around internally, you can use an internal TLD - .local is reserved for mdns, Avahi, etc. so that’s fine… personally, I use .home
I use pfSense, but I presume that OPNSense has the same function in DHCP to provide the Domain Name in there, so any static mappings will respond to thing.home
I also have HAProxy to resolve external httpS://IP:Port to an internal http://thing.home (note: no S internally)… this simplifies my setup, and I presume it could work internally too, but I’ve not set it up as DHCP solves that for me.
I don’t use containers, instead each thing is it’s own VM, or physical machine, so I don’t know whether NAT (on proxmox) would resolve your issues with everything’s on 1 VM…?

















Yeah, I’m not a subscriber - I don’t have a YT account - but if I did, I’d be down voting and writing comments like “so… where’s the content from your click bait thumbnail?” 😉
Edit: I’d also add something like “my subscription? You’ll never guess what I did next…” 😉