I'm not sure how many people used DSR in its original form - it basically let you run games at as high res as you wanted, and downsample to your native res. So you could play a game at 4K on a 1080p monitor, and it would look quite smooth. It's the original form of antialiasing really
It never really took off, I guess because the downsampling algorithm was not perfect. If you could run at exactly 4x res, it would work, but you'd have problems running newer games at that res.
Enter DLDSR which throws machine learning into the mix. It lets you run at partial multiples - so like 2.25x resolution, and uses ML to downsample and the results are AMAZING.
I haven't seen such a huge leap in graphics quality just from software, since DLSS. And yes, you can upsample to a higher res, use DLSS to render at a lower res, and upsample back to your native res. And the results are fantastic! It gets rid of all sorts of weird issues you'd normally see at lower resolutions
This feature isn't talked about much so I thought I'd start a thread. I think a lot of people are sleeping on it, but IMO it's worth enabling on just about every game you play, especially if you have performance to spare. I knew a 3070 on my 1080p monitor was pretty overkill, but with DLDSR it makes full use of the extra power with a huge improvement in quality.
Digital Foundry does a great job of explaining it here, with TONS of examples including combining it with DLSS