The Todo.txt format documented on GitHub.
I converted in 2019 to todo.txt and I have been tracking my tasks using simple a text file ever since. The text file is weekly commited to a git repository.
For time tracking I use a file per customer with a special tag
I have built a few scripts around the simple file format to extract reports and some more statistics.
In Visual Studio Code, I am using the extension todo-txt to highlight the projects and tags