I tried to make it work best for both Node.js runtime and web browser.

The official implementation is actually sqlite3, and there are at least 2 packages built on top of it -- sqlite and TypeORM. There are also other packages that can run SQLite including better-sqlite3 and sql.js.

I am talking about git branch and git worktree add; and also, git merge on GitHub website.

Apparently, even with creating WordPress theme, you don't really have to learn PHP much.

The only way to learn PHP well seems to be by creating a new CMS. Although, you might learn a little with some CMS, such as Bolt CMS.

This is a thing that can be done easy way, if you strictly follow these steps. The downside of DigitalOcean, is that if you messed up, no one will help you debug.