For an open doc, you can use Image > Image Size, ensuring that "resample image" is OFF and then change the resolution to 72 PPI. Then use (Legacy) Save As/Save a Copy to retain the resolution metadata. The size will remain 2048px.
If you use Export As/Quick Export, then the resolution metadata is removed, some apps may show 72ppi, others 96ppi as a default for missing resolution data. The size will remain 2048px.
If you use Export > Save for Web (Legacy) then the resolution metadata is removed, some apps may show 72ppi, others 96ppi as a default for missing resolution data. The size will remain 2048px.
Or another option, you can change the resolution metadata value of 300 to 72 in the following script, it only works on JPEG files:
Photoshop version:
Bridge version: