CI4 and wp in shared hosting

sure, if you're using the shared hosting, and uploaded the wordpress on public_html folder, then you can create a sub folder in it for CI4.
But we need to modify the index.php file, you have to move it from public to outside and edit the location loader in the index.php file so that when you point the url to that folder it will automatically run the index.php

with add on domain approach, which can be configured via cpanel, where each sub domain is a web app and for all intents and purposes separate you don't have to do anything except edit where root is for each sub domain. For Wp that would be the sub domain itself, whereas for CI4 the root would be public directory .

Thats exacly my live set up

yeah, if on the hosting CP had the way to edit, it's beter to config in the cpanel   but i have some client that their hosting does not provide this function, so i have to modify it for the case