First, SB6190 has the Intel Puma chipset, not good for latency, I realize that isn’t what you’re asking about but the point is you don’t want this modem. For near 1 gig speeds, I would look at DOCSIS 3.1, something like a refurbished Arris SB8200 or whatever D3.1 brand/model is least expensive and is supported by Comcast/Xfinity will work just as well.

The 800mbps is only gonna happen thru a wire and WiFi performance is gonna be based on your environment. I might start with tuning the channels and channel width your WiFi uses. For 2.4 only use the least congested of 1,6 or 11 and 20mhz channel width, for the 5Ghz, any least congestion channel using either 40mhz or 80mhz, depending on which works best for your devices. You can use WiFi Analyzer on Android to show channel congestion.

Do you have any computer with a wire that you could connect directly to the modem and do the zoom calls to see if the same thing happens? Essentially we’re tying to remove things to try figure out what might be causing the issue.

200mbps is your download speed, what is your upload speed? (zoom needs upload too).