You might want to pick up a course on using google, cause the first hit on "julia package manager" is the documentation: https://docs.julialang.org/en/v1/stdlib/Pkg/

"WTF does `activate .` even do?" If you then read it, it says "If you are ever stuck, you can ask Pkg for help:".

    (@v1.6) pkg> ?activate
     activate
     activate [--shared|--temp] [path]
     
     Activate the environment at the given path, or the home project environment
     if no path is specified. The active environment is the environment that is
     modified by executing package commands. [...]

Also the docs tell you in a highlighted blue bubble that if you don't want to use the "REPL-centric workflow" there is also the API:

> This guide relies on the Pkg REPL to execute Pkg commands. For non-interactive use, we recommend the Pkg API. The Pkg API is fully documented in the API Reference section of the Pkg documentation.

Most other language have cli gools like `gem` or `cargo` and if you're in a directory with a Project.toml why do you even need to remember to do that all the time?

If you're in a directory with a Project.toml do

    julia --project

and it's activated.

The downside of a separate cli tool is that it's unclear what julia version you're using. E.g. pip vs pip3.

You can expose it as a CLI tool if you wish: https://github.com/fredrikekre/jlpkg