XR1000 throttling speed (ONLY on Steam)

[RevyRevv]

Hi folks, hoping to get some WiFi wizards to take a peek at my issue. Currently everything else is great about the router and the features that come with its DumaOS 3 and all... Except it can't download from Steam. Every other facet of the internet works fine, download from other services perfectly fine. Steam, no.

So. I have a Netgear Nighthawk XR1000, connected directly to a T-Mobile 5G Home Internet Gateway. I have enabled IPv6 passthrough and the QoS auto enable option. No other changes made so far. Using the T-Mobile built in WiFi is slower overall but I get regular speeds on Steam downloads (20MB/s or more), but if I try it with my router instead which is faster everywhere else I get like 350kb/s

My PC is on Zorin OS if that matters, but I've seen from Google's people having this issue on Windows as well but answers vary so wildly I figured I'd come to the source.