You have been lucky the developer has released the documentation for the codes to address the I/O Modules, which appear at first glance to be fairly generic DIN mounted digital/analog 24V input and output multiport devices.
I presume the 8 volts on the serial port should be able to be decoded by a simple RS232 interface which is +/- 12volts for true RS232 and not 0v/+5v for cheap Chinese knockoffs. Alternatively, it may be a RS485 bus.
English is my first language so I have difficulties reading the Dutch notes in the diagrams, but they look to be modules that are driven by commands over the interconnected serial bus according to the English pdf file you have linked to.
Your challenge is to examine what is connected to each port on these devices, and what commands related to that device are used for command and device response.
You should be able to build a state lookup table that you can then convert to Python to make a driver for your system.
Alternatively, you could dangle the prospect of widespread adoption by the HomeAssistant community to the developer to entice them to whip up some code to communicate to the devices, as they already have a deep understanding of command flow, and just need to re-code it in HomeAssistant format.
[See update: Not needed]Using a cheap ESP8266 or ESP32 as a serial to WiFi interface in straight through mode as a two way UART would be the missing link that could supplement the Netconnect ALF-NET-LAN Ethernet to serial interface modem device. Just make sure to match the baud rate, etc on both ends to suit. The Chinese make many forms of this serial to Ethernet adapter, mostly using a Linux firmware to drive a chip to configure it via a web interface for the correct parameters. In your case, it is well integrated to the power supply module and the common data bus interconnecting each module via DB9 serial connectors.
An interesting challenge and thanks for the detailed information you have posted that will be of immense help for others that may be challenged in decoding this setup.
Update: On reading the other pdf with app documentation, the hard work has already been done, and a JSON file with appropriate contents would be the way to drive this over your existing local internet connection, without any further serial interface. Pull out your Python editor and start coding!
Example given uses:
IP Address: 192.168.0.50
Port: 1470
Sniff using WireShark or something similar, issue commands to your system from the app and observe the data flow both ways. Look for bit/byte patterns, and imitate them for control from HomeAssistant.
You already know what devices are connected to each digital and analog port, input and output, as you installed it yourself. The rest is just logic to issue the right bitwise command and decode it to digital switches in HomeAssistant.
Create a list of each device connected to each port, what it is used for, and what data flow you expect to drive it and monitor it. Use this as the basis for device naming in HomeAssistant.
Going back and examining your contents of the folder on your Windows hard drive at C:\AlfaStar\ and subfolders will also give you more useful information (including the db and logger file). That directory listing I asked for in an earlier post may provide hidden clues to explore further.
A closeup photo of the various ICs on the NetConnect, and input and output boards to identify the interface chip numbers would be very interesting for me. The five on the input board, the four on the output board, and the two big ones on the NetConnect board. Any closeup photos of the inside of the controller/power supply module to the far left?
What devices do you have connected to these controllers? Infrared, motors, switches, buttons, relays, lights, alarms? Are there any further interface boards between each device and these modules? Make and model would help for sleuthing. What kind of wiring do you have connecting them? Twisted pair, etc?
Does the developer have Windows documentation also? Linux/Python?
Give us more: You are tantalizingly drip feeding us info and keeping us on edge, waiting for the next installment!!!
