With a fresh installation of Mathematica on a new raspberry pi 4, I find that the links to help and documentation and the Wolfram site are all erroneously prefaced by "/home/pi" which causes an error since the links are then not found. I tried 3 modes of installation : (i) rpi menu add software (ii) sudo apt-get ... (iii) running the installation shell on the Wolfram rapberrypi site. All gave the same result: succesful installation but this same problem. I would be glad of any fixes (e.g. in Options) or ideas how to correct the installation. Is there some way of seeing what variable it is that contains this information, which is erroneously set to the default installation place for Wolfram-Engine, corrupting network links from http://.. to /home/pi/http://.. ?
The solution was to reinstall xdg-utils with
sudo apt-get install --reinstall xdg-utils
(many thanks to ilian for linking the problem to xdg-open rather than Mathematica).