Moreover on Android you still can have 10 different Google accounts on one phone all from different countries for downloading region-locked apps on Google Play. Though recently Google started to break it by changing account region countries nilly-willy. Yet you can still register as many accounts via Chrome as you wish really without extra gmail accounts just by using own domain redirect via cloudflare or something.

On iOS installed apps are locked into specific Apple ID they been downloaded with, so you might have issues with e.g WhatsApp. Still possible to download region-locked apps with non-primary AppleID, but it will sometimes ask to re-authenticate with said AppleID to keep it updated so it's cant be just throwaway.