Apps need a local server to work (especially if it writes to a local database), or be shipped in some kind of executable file format for the OS. As someone who can't code native apps but is decent enough in PHP, I've discovered that the way to solve my own problem is to run a bash script that loads an Apache server, then loads the index.php file of my app, all of which is stored locally on my hard drive. Works on mobile too, although I have to manually launch an Apache server first through termux.

Modern computing badly needs the ability to support building our own local apps without a remote web server dependency. This is how computing worked in the pre-internet age. HyperCard could connect to a database as could Filemaker Pro. Windows had something similar where GUI-based apps could read/write to an Access DB. These tools have been deprecated and only live on in some subscription-based SaaS.