If you are rendering at 4K then having it downscaled to 1080P then yes it will look better. If you do it for games, for example, it will make it so you wont need AA as it rendering it higher than the native resolution.
If you record something in 1920x1080p then upscale to 4K it wont be as good as 4K. If you render and record at 4K then upload in 4K it will look as good as 4K for those who can see 4K (they have 4K monitors).
If you record something in 1920x1080p then upscale to 4K it wont be as good as 4K. If you render and record at 4K then upload in 4K it will look as good as 4K for those who can see 4K (they have 4K monitors).
If I upscale it to 4k while using 1920 x 1080, will it look better than something say, rendered in 1920 x 1080?
On one hand it seems like it would but on the other hand... I don't know.
If you are rendering at 4K then having it downscaled to 1080P then yes it will look better. If you do it for games, for example, it will make it so you wont need AA as it rendering it higher than the native resolution.