Maybe I was not clear, but I do not think that you understand what I was trying to say with the second part of my last message.
Assume that multiple VIPs are setup and there is a load balancer IP for the SFTP entry point (eg: 192.168.1.40:22) and a different load balancer IP for the Forgejo SSH entry point (eg: 192.168.1.50:22). My local DNS can be setup so that sftp.my.domain points to 192.168.1.40 and ssh.forgejo.my.domain points to 192.168.1.50. When I make a request within my network, the DNS lookup will appropriately route sftp.my.domain:22 to 192.168.1.40:22 and ssh.forgejo.my.domain:22 to 192.168.1.50. I believe this is what you are recommending and exactly what I want. I will need to get the multiple VIP part of this setup worked out so I can do this.
However, this will not work when the traffic is received from outside of my network even if the above configuration is setup correctly. If you were to try to connect to either sftp.my.domain:22 or ssh.forgejo.my.domain:22, your traffic would be routed to my public IP address. My firewall/router would receive the traffic on port 22 and port forward the traffic to the single IP address assigned to that port forwarding rule. When k3s receives the traffic from my firewall/router, k3s will not have any SNI information (ie: it will not know whether you were using sftp.my.domain or ssh.forgejo.my.domain - or any other domain for that matter). Even if I were able to setup multiple port forwarding rules for port 22 on the firewall/router, I would still be unable to appropriately route the traffic because the firewall/router would also not know if the traffic was intended for sftp.my.domain or ssh.forgejo.my.domain. As a result, at most you would only be able to use one of the services because external traffic for both sftp.my.domain and ssh.forgejo.my.domain will be routed to the same IP address and k3s would have no idea what domain (if any) is being used.
There are a few solutions (eg: use different ports for each SSH or non-TLS trafficked service, wrap the SSH traffic in TLS to give k3s SNI information to route traffic to the appropriate endpoint, configure SSH on the node to route traffic to the appropriate IP address based on SSH user, require each client to use the local network or VPN, etc.), but none of them are as seamless and easy as routing TLS traffic which can use SNI information.
I am comfortable routing traffic via domain name through a reverse proxy. I am doing that via Traefik and can setup rules so that different sub-domains, domains, and/or path is routed to the appropriate end point (IP address and port). The issue is that k3s does not receive that information for SSH traffic since SNI (ie: the sub-domain, domain, etc.) is not included in SSH traffic. If SSH traffic provided SNI information, this issue would be much less complicated as I would only need to make sure that the port 22 traffic intended for k3s did not get processed by SSH or any other service on the node.
If I were to setup a DMZ, I think I would need to setup one unique public IP per SSH service. So I would need to create a public DNS record for sftp.my.domain to VPS#1's public IP and ssh.forgejo.my.domain to VPS#2's public IP. Assuming both VPS#1 and VPS#2 have some means of accessing the internal network (eg: VPN) then I could port forward traffic received by VPS#1 on port 22 to 192.168.1.40:22 and traffic received by VPS#2 on port 22 to 192.168.1.50:22. I had not considered this and based on what I have seen so far, I think that this would be the only solution to allow external traffic to access these services using the normal port 22 when there is more than one service in k3s expecting traffic on port 22 (or any other port that receives traffic without SNI details).