Help. I'd like to build a system with SQM but

[moeller0]

@bingbangbong

That much I have learned that there is no compatible SQM firmware for Fritzbox 6591 router/modem

Currently, no cable modem is supported by OpenWrt as far as I know and that is likely to stay that way given that DOCSIS ISPs need to trust the modem. I would guess/hope that you can configure the fb6591 into 'bridge-mode' solving your modem problem. And then you need a router capable of traffic shaping your 300/20 link. That certainly rules out all the old MIPS based routers and likely also some of the newer ARM based routers as well. Even though 300 < 500 I recommend to read the following thread as it seems relevant:

So you have 500Mbps-1Gbps fiber and need a router READ THIS FIRST

It's such a frequently asked question over the last few years that we really need a post we can point people to. So your cable company rolled out 500Mbps or 1Gbps download speeds, or you have 1Gbps symmetric fiber (GPON/EPON) from ATT or Centurylink or Orange or whoever. You realize your old all in one router from 2009 is not up to the task of handling this, but hey by now stuff should be cheap and available that will handle your new fiber connection right? So you want advice about a router for…