That’s why this is not working. If your PFsense does your OpenVPN, your Nethserver must use that as gateway!
You could provide such critical information right from the beginning.
My mind reading capabilities are rather rudimentry, and long distance and foreign languages don’t makes things easier (Joke !!!)
Easiest would be to set up your OpenVPN on NethServer, using it’s own RED WAN connection. You do need a route on your PFsense pointing to the OpenVPN network (192.168.70.0/24 if I’m correct) and using the NethServers LAN IP as Gateway.
Remove the entire OpenVPN setting from your PFsense!
My 2 cents
Andy