I just went through the entire topic, and haven't seen this being mentioned anywhere. That's slightly disappointing, I would love to see a fix for this. Let me try to explain what's going on. I don't remember seeing this in v2.0, so I know it's a beta thing.
Before anyone says it's my net, I get a ping of 24, when I ping qcsalon.net. Before anyone says it's my hardware, I tried on an 8th gen i7 running win10 21h1, a 2017 macBook air running windows 8.1 bootcamp, and 2 windows 7 machines, both being sandy bridge based CPU's. Meaning, what I'm about to describe, is not due to low end hardware, either.
Here's how to reproduce it. Do uno with something like 3 second intervals. Find a fast player, who can spam their cards insanely fast. (The faster the better.) Now at this point, if you're on windows 10, or windows 8.1, you're going to lose NVDA completely. Now you may think it's an NVDA issue. Except... I tried messing around in the advanced dialog, I even tried python 2 NVDA on win7, (more on that later) the lag spikes consistently stay there. If you do 5 seconds, or no time limit, the problem is not so bad. I can provide recordings of what I'm talking about, since it's super easy to reproduce. Now here's the problem.
Same NVDA config, same playroom beta folder off oneDrive, same NVDA alpha, with the same add-ons installed, even on my crappy windows 7 celeron, I have absolutely no lag spikes. As soon as I get on windows 8.1 or 10, lag spikes appear. Yes, I'm using direct audio with all 4 systems in question, (changed it in the playroom options). I guess what I'm trying to say is this. If one is using windows 8.1 or 10, and does 3 second intervals in uno, lag spikes will kill speech entirely, but retain client sounds. As soon as one gets on windows 7, no matter how crappy the hardware might be, it runs rock solid, nicer than ever before.
My win10 and win7 run high definition audio from microsoft, the other windows 7 is on IDT, and the mac is on cyrrus logic. That is to say, what I'm describing is not due to audio drivers either. I get rid of that garbage first thing on my systems. It's something between beta and win10/8.1, seeing as microsoft high definition still has lag on win10 and not on win7. Now something else worth mentioning, when I downgraded to NVDA 2019.1 on my win7, (that's how I tested initially) there is no difference between running that, or latest alpha on it. Yet the same alpha, as mentioned above, lags on win10. Interestingly enough, JAWS 2021, on all 4 systems, lags with uno regardless. That's a JAWS issue, though. Even pressing up and down arrow feels sluggish, hence I haven't touched upon JAWS much. I'm thinking it's a JAWS thing, v2.0 wasn't much better with it either, from what I remember.
I don't know what causes it, (I'm not a dev) IDK if there is a fix for it, I did my troubleshooting steps to figure out the patterns and causes. If I can be of any help, if I have to provide recordings, or test certain situations, someone please let me know, and I'd be glad to. In the meantime, whoever can, use windows 7, or even XP if you have, for uno purposes. Ideally a physical, not a virtual machine.