Apache should be listening on port 80, and on port 443, but webmin is a standalone system, and it'll run without Apache, as it has it's own mini webserver, specifically for webmin.

Also if you have Apache running on port 1000 for SSL and you have webmin running too, there will be a clash, so I would suggest you re-assign Apache ports back to default ports 80 and 443, and leave webmin at port 10000, and only open TCP ports 80, 443 and 10000, (and SSH if needed) in the router.

I run a home server with Apache, Mysql, and PHP 7.0 along with Webmin, and I can access Apache and webmin from the WAN with no problems.

You don't say what OS you're using for the server running webmin and apache, if you're using headless Ubuntu 18.04 LTS server like I am, then use the CLI and check if webmin is actually running, using:-

su systemctl status webmin

if there's a port conflict this will tell you.

When I first set up my server, I installed a clean install of headless Ubuntu 18.04 LTS with no other packages, then using wget, I downloaded and installed webmin, then using https://localhost:10000 to set it up, but the apache module told me that Apache was not installed so I installed it, along with PHP 5.6, 7.0 and 7.4, then I installed MySQL, then I configured SSH for non standard port, and opened the ports I needed for SSH, Apache (80, 443), and webmin 10000 in the router, and I tested it using my cellphone with WiFi disabled so it used mobile data, I can access webmin on port 10000 and the Apache default page on port 80, using my domain name, I can't use 443, because I don't have a valid SSL certificate yet.