Create Subdomain > proxmox.yourdomain.com

Create DNS Record (Domain-Provider)

First of all, we create a DNS record for our first subdomain with our website provider.
Since I run my domain via Cloudflare, I will also create my first DNS record there.

Open your DNS-Record-Area
Create the record with the following values
Save and Apply

Connecting to OPNsense-WebUI

Open and Login to opnsense.yourdomain.com

Create NAT-Rule

Go to Firewall > NAT > Port Forward
Add Rule by clicking the plus-button
Enter the following values
Hit ‘safe’ and then ‘apply’

NATrule-Settings

Edit Redirect entry

Interface - 102_proxy
Destination / Invert - false
Destination - 10.10.10.0/32
Destination port from - (other) 8006
Destination port to - (other) 8006
Redirect Target IP - 10.10.10.0
Redirect Target Port - (other) 8006

Connecting to NGINX-WebUI

Now you can access the web interface of your proxy manager with your browser.

https://proxy.yourdomain.com

Create Proxy host

Go to Hosts > Proxy Hosts
Click green Add Proxy Host-Button
Now enter the following values
Click Safe-button

Proxysettings

Domain Names - proxmox.yourdomain.com
Scheme - https
Forward Hostname / IP - 10.10.10.0
Forward port - 8006 (Proxmox-Port)
Cache Assets - false
Block Common Exploits - false
Websockets Support - true
Access List - “Publicly Accessible”

If the host you have just created has the status "Online", everything has worked and you can reach your proxy manager at proxmox.yourdomain.com.
You can now close the Browser with yourip:8006