Your question is rather non-specific, so somewhat difficult to answer.
PlatformIO is the best solution, or adding URLs to the github page for the actual library you used (handy if you want to share your code with others anyway).
Whenever I download a .zip library I keep a copy in a separate folder, so I can install the same library on multiple machines if necessary.
None of this helps if you have a project where you’re trying to track-down the actual libraries you used for a specific project, but in that case you may find this approach useful…
Pete.