Bandwidth of 25Mbps is recommended at the high end for 4K TV streaming, with Netflix stating that it needs15Mbps. With steaming services moving to HEVC/H.265 video encoding, the norm will become 15Mbps. Depending on the screen resolution, Zoom requires 6Mbps at the high end for 1080p.
The rest of your Internet usage looks relatively low and sporadic that should not cause the speed to drop down from 50-150Mbps down to <1Mbps. Have you seen a correlation between when the speed drops and when 4K streaming, Zoom, file transfers are occurring?
You can look up “Data usage” in “Settings → Connections” on your S10 5G during slowdown to see if mobile data usage goes up quickly every minute or so (50Mbps for 60 seconds = 375MB).
I don’t think T-Mobile and other wireless providers guarantee minimum speeds and speeds may vary at different times, even for 5G. QoS will increase throughput of high-priority traffic, but low-priority traffic will get worse.
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