Can it work at 1440p? other say yes, BUT beware there is probably some context to that. The 1660Super is plenty/fine. So, you need to make sure you are NOT using CPU intensive filters/effects, etc. Beware things like chromafilter/green screen which is CPU intensive (I believe). You have to do some research, on whether re-scaling is done by GPU or CPU, probably best to avoid, but do your own checking. This whole CPU vs GPU is something I'm aware of, but haven't need to dive that deep into. There are comments in this forum that clarify for certain things. And you should probably plan to build up your OBS Studio streaming PC slowly, checking hardware resource utilization as you go, so you know which settings have which impact.
The issue is that CPU can at most run Win10 with Extended Security updates ending in October. Now, if you really know your way around Windows OS security, and avoid any/all things that create a security risk/exposure on that streaming PC (no browser sources, no streamlabs plugin, etc) , then maybe you might be ok. maybe. If really stuck on not getting something that will continue to get Windows security updates, I'd be seriously inclined to format (dual boot to test/start with) that old computer with Linux
I say this as someone who avoided that PoS Win11 until just recently with a new computer (and am still running a number of Win10 PCs and VMs with ESU.. all of which I'll decommission (or take off network, archive only state) later this year. No, I don't like Win11... typical of last 25+ years every other desktop OS PoS from M$. time will tell if M$ truly gets the message and clean up some of the worst of the nonsense (much of the rest of already somewhat tolerable, imo, with decent registry edits).
But for older hardware I wish to keep using, I'm converting those to Linux