In his videos Andreas mentions the motivation for creating Jakt was wanting a safe productive language for developing SereneityOS and its GUI Apps for the long term future as he didn't believe the trajectory of C++ was going to be suitable and found other languages unsuitable for adoption in SerenityOS so he teamed up with JT to create a new one without C++'s unsafe footguns, initially transpiling to C++ so it's easily integrated into SerenityOS build system and able to access their existing C++ libraries.

They're still actively developing inheritance support which I believe is the last remaining feature before they can start creating SerenityOS's (OOP) GUI Apps with it [1].

[1] https://youtu.be/47svsnd7HIQ