Any way to create/use IOS applications on iPhone without having to publish to the App Store?

If this is a copy post or in the wrong thread, I apologise.

Among the inordinate amount of other interests and projects I have, I’m wanting to make a bunch of “mini-apps” like customised calculators and organisational apps for my own personal use, and being able to operate them on my mobile device when my laptop is inaccessible would be a huge plus.

However, most apps seem to have to go through the App Store first, and as far as I’m aware, it’s a $100 fee per year for developers. Since I only have recreational interests, not commercial (though open to change), paying the fee isn’t very ideal for me.

Basically, I want to create my own apps to use “offline”, but I don’t know if there’s any other way to install them onto the mobile device.

I’m not very knowledgeable in software or programming yet, sadly, so I have yet to try any elaborate workarounds.

I just want to maximise my productivity through automated applications, but I keep getting the feeling that all the requirements to do so are getting more and more intensive, and the list of tasks longer and longer…

Or maybe what I’m asking is still too advanced for mobile development right now, and PC work will have to do…