Photoshop saving all images at 300dpi

[Vibhu29993]

So, my photoshop is behaving very weirdly.  I'm changing the dpi in Image>Image Size from 300 to 72 and it is resizing the image. But, when I save the image it automatically changes the dpi to 300 but with a new image resolution. I am using Adobe Photoshop 2020 on an iMac. Any solution? 

[D Fosse]

Please post screenshots of the Image Size dialog before and after.