I don't know is it possible to dstnat/re-route the multiple virtual host (IP > DNS Settings > DNS Static) that actually has 1 public IP to multiple internal ips. Might Not load balancing (not similar to haproxy since HAProxy only for web services), but more to routing.

Example,
if User open web browser at sub1.domain.com, he will redirected to Server A's webserver.
if User open web browser at sub2.domain.com, he will redirected to Server B's webserver.
if User access the SSH at sub1.domain.com, he will redirected to Server A's SSH service.
if User access the FTP at sub2.domain.com, he will redirected to Server B's FTP service.
and so on.

Here's the diagram I plan to do but is not sure is it valid/possible or not. Or is there any way/method around?

it would be an awesome feature but unfortunately as far as I am aware it is not possible.
I also use HAProxy for such cases

ROS doesn't provide reverse proxy service, you will need to setup it manually on some server or in ROS container, there are many choices like HAProxy, Nginx, Apache, Caddy...
In ROS setup nat for HTTP/S ports to IP of reverse proxy and rest is in reverse proxy configuration depending which is used.

You cannot use HTTP reverse proxy for non HTTP protocols. So for SSH and FTP you will need to find another solution, maybe some SSH/FTP server which provides this functionality and setup nat to its IP for these service ports.

Another option is buying Linux VM from VPS hosting ( each has its own public ipv4, virtual machine ) - you making SNAT/DNAT to your Router.
Solution for the "need more public ipv4".

Zero Trust