It's under Save A Copy. That's where you find jpeg, and all other formats that don't support every property of the original file. This is new from 22.3, but there is a preference setting to revert to the old Save menu.
Export is for web/screen/mobile devices, where ppi is irrelevant. So the ppi metadata are stripped from the file altogether. A file out of Export has no ppi, not 72, not 300. The 72 number appears when the file is reopened into Photoshop, and a default value of 72 is assigned. Other apps might assign other defaults, like 96 in all native Windows apps.