I did some tests with the firmware you sent me but nothing worked, I also tried downloading from steam, sometimes the download is recognized, sometimes not but nothing changes, if the network is saturated with a few downloads the qos it doesn't work, I tried both in dhcp and in ppoe, I set the exposed host (dmz) on the fritzbox to the ip of the netduma router (the only device connected) the netduma and connected in this way:
wan port of the netuma that goes into the lan port of the fritzbox, I don't know what to try, it's useless like this, I don't know what it could be, the qos doesn't work in any way that I've tried, the prioritized traffic is too little and it freezes, in the image I attached the stream to work, it needs 10 MB and those in the photo were the maximum MB it reached but it's always almost between 0 and 1 MB
the fritzbox is a 7530