Sorry I'm lost. How do you have 100/100? I thought zen was 100/20 on full fibre? Still shouldn't be a problem but I'm a bit confused here. Is this a city fibre tier?
What upload speed tests are you seeing? Does it get any better with your video off?
Also, what are the specs of this PC? It might be the computer is too slow to encode the video and Teams thinks it's a network issue when it isn't.
Zen Full Fibre 100mbps download and 100mbps upload (i've just ran a speed test and I'm getting 102/146)
PC is a Microsoft Surface (Snapdragon CPU I think) running Windows 11
Presumably WiFi connected rather than cabled ethernet? Then running over a powerline ethernet link back to the router?
If so this is basically not a recipe for success. I mean it's going to work but the performance *can* be wildly variable as both WiFi and powerline aren't guaranteed throughput and latency, as alluded to above.
Your best bet as noted in several posts is a direct cabled connection from the client machine back to the router - although that may be impractical, but would rule out other issues in your local network.