I am planning to install BI on a Dell Optiplex 8-core i7 9700 and eventually eight cams. I have a Windows Server license I am willing to burn if there will be a benefit over using W10. Any thoughts?

So while not an OFFICIAL answer... I would say go with Win Server then. I have seen posted in places that it's ideal to use W10 but I too had/have license access to Server2019 and it works great for me. Really the OS's are very similar other than additional capabilities baked into server, many of which you can disable if desired. It's running great for me, I still get Intel hardware acceleration (and thats also using VMware ESXi).

Also, with experience in the IT field.... we're running/using an application that serves users - potentially multiple users - remotely and has a web interface, etc. It should be on a server platform.

Plusses and minuses on server. I am running BI on a Dell R710 server with dual Xeon L5520 CPUs and 48GB of RAM using Windows server 2012r2. It is also my file server, domain controller, and a very lightly used web server.
One down side to using server hardware is that often the built in video and audio capability is very limited (don't normally need much on a server). Since you are not proposing using server hardware, that is not an issue. It is for one piece of software I run.
Using server software (without using most of the server capabilities - domain controller, file server, etc) likely will result in far less background crap that goes on with end user operating systems. So I would agree with Matts1984 (for a lot of the reason he stated) and go with the server OS.

Jim

Thanks for the responses. I was not going to mention ESXi, but since it's already on the table, how does BI do as a VM? I have a two-server ESXi cluster with iSCSI storage that is now only being used to host a couple DCs. It seems BI might run better on dedicated hardware, but it would certainly be easier to manage in a VMware environment.

I have no complaints. I know there are definitely guides and other opinions out there that say otherwise. Intel acceleration works just fine for me. It might be harder to get Nvidia GPU decoding to work with VMWare but I've read mixed things about GPU decoding anyway - Intel seems the way to go. If you can run advanced enterprise services in vmware, large SQL servers, all kinds of fancy web apps, I don't see why it's not possible. I think it may come down to comfort level.

You mentioned 8 cameras on a 9th gen i7. I think if configured properly with sub streams, D2D recording, and no insane frame rates - that should run excellent even if you opt to add some more cameras over time. My CPUs, while they have a lot of cores, are over 10 years old at this point and I couldn't be happier with performance. I'm certainly not a VMWare expert but it made sense on my end to try it first anyway, and it does give me some added flexibility this way. It sounds like it would for you too. I should also note that I did NOT have to do anything real fancy in ESXi to get it to work.... everything is standard config to the best of my knowledge. I'm on fully patched 6.5 if that helps at all.

I'm curious if your thinking of running it on server core. I'm currently running mine on ESXI on a HP DL380 Gen8 20 Core E5-2680. Storage Wise I have a PCIE NVME 1TB Storage Card for New Video, 1TB Raid60 Storage for other VM Stuff and Windows OS. Then for long Term I've got 40TB ISCSI. I also have an Nvidia GTX 1050 working and am thinking about switching it out to a Server Nvidia Card. This is for a home setup. I've got 8 POE Camera's all 4k. Ranging from Axis to Hik cams. Getting Nvidia's to work on ESXI isn't to bad. If memory serves me correct you have to install the VIB, Edit card as passthrough and of course you editing the VM's advanced options and create an entry for hypervisor.cpuid.v0 = "FALSE".

Currently I'm running Windows 10 and was going to install either 2016 or 2019 server OS as I don't like running desktop software for non desktop tasks. I really wish BlueIris was coded for Linux but can't win them all. But figured I'd just do Server Core but I've ran into some applications that don't work without a GDE. Some we've found we can do server core and start with server core with Server-Gui-Shell roll and after getting up and running disable the GUI. Then enable as needed to make config changes to BlueIris.