I have a few selfhosted services, but I’m slowly adding more. Currently, they’re all in subdomains like linkding.sekoia.example etc. However, that adds DNS records to fetch and means more setup. Is there some reason I shouldn’t put all my services under a single subdomain with paths (using a reverse proxy), like selfhosted.sekoia.example/linkding?
If your router has NAT reflection, then the problem you describe is non existent. I use the same domain/protocol both inside and outside my network.
Does NAT reflection still work if your PC is connected to a VPN?
Depends:
If you have your VPN setup so it sends all traffic to the internet, then your request will pass through the VPN server, then back to your location from the internet.
If you have your VPN setup to exempt LAN traffic, then if you specify a local IP, your traffic will stay on your LAN, however, if you specify the domain, the VPN will almost certainly continue to treat it as internet-bound traffic and route it through their servers. This is possibly avoidable if you also put your own IP on the exempt list, if that is a feature.