OBS emulates mouse pointer. Internally, OBS grabs only position of the pointer and draws picture of the mouse pointer at this position over the desktop picture. This is because of how cursors are rendered in the OS itself (accelerated by GPU). So, there is special setting in "Display Capture" source of OBS to not capture the cursor - this should help with "normal" not zoomed pointer.
There is script that may help to enlarge only OBS source (Transform it) with hotkeys. It was mentioned in:
I'm recording some training videos for a YouTube audience with a talking head in the corner. I'm using DroidCam OBS over home WiFi for the video source. I can see the video on the Android phone is high quality. When I expand the talking head in OBS Studio it has deteriorated but is "acceptable"...
obsproject.com