Hi,
Does anybody know
how a package (in a project) could be available in all (other) projects !
or
do I need to install the new packages EVERY TIME to new projects (although I had downloaded / installed them in another project) !
(as I’ve downloaded/installed XR Interaction Toolkit (in a project), but when I created another project, I couldn’t found it there (in package manager)
Thanks for the help
The “download cache" is shared between projects, which means the download should happen only once.
As far as having to re-import the packages in different projects, this is very intentional. Sharing all the packages between all the projects would cause massive headaches, conflicts and performance issues.
That being said, the project creation flow could certainly be improved to make things easier. This is something that is constantly being worked on by the team.
As soon as we can create custom project templates with predefined packages (maybe that’s already possible?) and those templates can be either installed locally or shared with a team, it would solve OPs issue. 
However, we also need to weigh this against all other issues that could be tackled. How many projects do users typically create? My company starts a new one every 6 months and I report a bug in a clean Unity project every couple of weeks, sometimes days, but these projects don’t need any configuration.
Custom project templates are not yet a thing, but as a workaround “empty” projects can be created from the command-line by passing “-upmNoDefaultPackages”.
As another workaround, users can create their own “template” by creating an empty project with whatever packages they want, and copy+open it from a new location rather than creating a new project from the Hub.
Beyond that it’s just not possible to install a package in a project and expect that package to be present in other projects without first adding it to those project. Packages are, by nature, project-specific.