How can I sync my custom plugin to all my devices?

What I’m trying to do

I’ve written a very simple custom plugin consisting of a single “main.js” and “manifest.json” file, just to automate some data insertion tasks and to apply some conditional formatting to text.

This plugin has 0 value to anybody except myself and contains private data, so it’s not really an option to publish it.

This plugin works well on the machine where I wrote it, but it doesn’t seem to get synchronized to my other devices like community plugins do, which makes sense. How then, do I go about getting my custom plugin installed on Obsidian on my phone and tablet?

If this can’t be done, are there any other ways I can customize Obsidian with custom javascript/css without using a plugin, that supports synchronizing between all my devices?

Things I have tried

Nothing, I have no ideas

And do you need it to synchronise? Isn’t it enough to install it individually on each device as it is written? Do some things in the plugin change over time?