I see that this is for MacOS. Isn't there a stock feature for screen recording, like on the iPhone, or on Windows (snipping tool can do screen recordings since Windows 10 or 11)?
I don't know about screen studio, but if I were looking for a way to edit screen recordings I wouldn't be searching for an "open source alternative", I would be searching for "open source software"
Defining your project as an open source alternative to another program is a mistake I think
OpenScreen and its ilk seem to have more features for post-capture editing though.