The cause of this bug could be fontconfig building the font cache at initial startup.
With many fonts on a slow system I guess it actually could take some minutes to finish.
During that time the Inkscape process would only be active in background (visible in taskmanager), using up 100% CPU time of one core, with the GUI start being delayet until building the cache is complete.
If I remember correctly earlier versions of Inkscape used to generate the fontconfig cache only when actually importing PDFs, so initial startup was not delayed.
The cause of this bug could be fontconfig building the font cache at initial startup.
With many fonts on a slow system I guess it actually could take some minutes to finish.
During that time the Inkscape process would only be active in background (visible in taskmanager), using up 100% CPU time of one core, with the GUI start being delayet until building the cache is complete.
If I remember correctly earlier versions of Inkscape used to generate the fontconfig cache only when actually importing PDFs, so initial startup was not delayed.