if you're your monitor is capped to 1440 stream 1440, however i dont recommend streaming 4K out of your 2K monitor because the performance cost per quality is detrimental at best, the quality isnt noticable as people will still only see a up-scaled 2K (fake 4K if you will)
HOWEVER, if you really want to you have to make a nvidia/amd custom resolution of 4k (3840 × 2160) and run that resolution to do anything, it may be very laggy but worth a try
