Hi @gsgmx,
Fistly, have you noticed the drop down menu at the top right corner of RStudio? It opens a menu similar to File - Recent Projects, but only your last 10 projects. Next to each project there is an icon that, when clicked allows you to open a project in a new session.
Secondly, I have an addin that might be of interest.
Most recently used projects addin
It's been a bit of a backburner project for about 4 years
, but I just updated it to work with RStudio 1.4.
So far I have only tried this version on Windows, but an earlier version did work on Linux.
I assign ctrl + P as a shortcut, and then I find it easier to use than opening the file menu.
Feel free to see if it works.