@Steve Bowman what NVR do you have again?
Ive discovered that IVS seems to be disabled on my 4208-8P-4KS2 NVR's. These are the ones I use for the HOA and I record 24/7 plus MD so had not really had the need for IVS, though I did have it setup and working on the one camera earlier this year just to see how it worked. The tab is still there, but its obviously inactive..
Apparently some firmware update in the past 6 months or so has disabled IVS, I think I saw a post about this now that I think about it, and it no longer appears as a feature on the Dahua website ... hmmm
My home HCVR7208 does do IVS but it is different than the IP NVR's in that it is all done on the DVR and not dependent on the CVI camera being IVS capable. I enjoy using Tripwire at the house and it works great.
As as sidebar, Ive found that Dahua seems to be cracking down on distribution of their high-end CVI products. They've introduced a bunch of new models this year, but can no longer be found by most AliExpress retailers or the handful of US retailers. The only CVI products that seem to be available are the low end and middle of the road stuff..