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).
Bufferbloat tests can be misleading, you only get bufferbloat when your saturating your connection. Gaming does not use a lot of bandwidth (maybe 2-3K), it does however, require low latency. Is your gamer WiFi or wire connected to the internet? If using WiFi try a cable.
Your not gonna get what you desire with consumer level "all in one" gear. You need separates (ie router and AP).
As a suggestion, look at PiHole to stop some things from reporting (also stops some ads and some malware)...not the complete answer though since, as already posted, your ISP sees all....
Once you get away from consumer level, look for routers/switches that support VLANs. For those devices that you just want local access to and not report anything to the mothership, you would need to create a VLAN with no internet access and place the IOT devices on it, unfortunately, sometimes you lose the easy "connect from anywhere" functionality.
Sorry, I don't know of any.
IMO not a good idea to use any VPN on LAN, except for remote access into it.
Any VPN will increase your latency. Playing thru remote access will kill your latency.
I would create another VLAN just for cameras with appropriate firewall rules. Allow Trusted into this "no-internet" VLAN but nothing to the internet. One way would be to figure out which ports the cameras use so you can add a firewall rule to allow communication to the NVR's IP. Another way would be to set the NVR on a static IP in the IOT and allow all traffic to it from this camera VLAN, (this is probably the easiest but not the most secure).
As a side note, I try to set as many things that I can on a static IP, it enables the use of firewall rules, also helps with normal monitoring.
As another side note - The Unifi APs support up to 4 VLANs (1 per SSID) - they also support the use of a SSID with multiple passwords which will allow connection to a VLAN depending on which password is used. It's a new feature and I haven't used it, so idk how well it works or other issues.
I would set up Trusted, IOT and Guest VLANs. Put all PC's, servers and NAS in it, all else goes to IOT (Phones, Tablets, streamers, cameras and NVR, etc). Create firewall rules to allow internet for all and let anything from the Trusted network to get to IOT and Guest, but block everything from IOT and Guest to Trusted (except for a couple exceptions). One exception is I don't see a printer but if you had one I'd assign it a static in the Trusted and allow all VLANs to get to it's IP. Another exception is I use PiHole (lives on Trusted) and I allow only port 53 (DNS) to those IPs, (I have 2 Piholes).
Your Unifi APs are VLAN aware but I have no idea on your router/switches (I assume at least the router is).
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.