Try https://gitjournal.io/ . It's open source and works very well for me. Don't forget to donate if you like it, the dev is super nice!

I've been using Working Copy [0] for quite some time and have yet to meet any limitations. It's a freemium business model (though the free version did have more than enough functionality for me until I wanted to push from my mobile device as well) but the one time $5 payment is well worth it in my opinion for how high quality of an app it is. It has some crazy features and crisp integration with the iOS workflow, I'd highly recommend it.

0. https://workingcopy.app/

I just use termux on Android; whether that counts as simple to use will depend very much on your personal preferences, but it was really easy in my opinion, and conveniently gives me the same workflow everywhere. You can also add shortcuts to your launcher and add some scripting if you want to make the whole thing smoother.

Beware, Termux + vim uses too much battery in my old phone

Give Termux a try: https://f-droid.org/en/packages/com.termux/

> I already have native git client and text writing application on my desktop

You can't just tell us you have a non-electron app and not tell us what it is, don't leave us hanging!