I would love to be 100% sure about this. I did this few years back. I know I searched on the internet on how the dat file should look like and came across that AMule uses these files. And explanation for all these fields can be found here.

That documentation is short but to quote the most relevant part:

IPs range , Access level , Description
Access level values lower than 127' are blocked IPs and values over 127 are allowed IPs. 

The thing is I don't know if this is a some kind of standard or not and I don't know if qBittorrent needs (and respects) those two other fields. Maybe it even ignores them, because why would an IP range would be in IP blocklist if not to block it? However, at that time I could only find that information, it did make my work any harder, it seemed to work, so I did not try to create and use a filter without them.