I do a little bit of everything. Programming, computer systems hardware, networking, writing, traditional art, digital art (not AI), music production, whittling, 3d modeling and printing, cooking and baking, camping and hiking, knitting and sewing, and target shooting. There is probably more.
The minority of Vivaldi is closed source from what I have read actually - specifically the stuff they have that makes its fancy UI work, but someone can correct me with a citation if that is not true.
They state that about 95% of it is available to be read where 92% of that is open source from Chromium, 3% is open source from Vivaldi themselves, and the last 5% that is not available to be read is Vivaldi’s UI.
https://vivaldi.com/blog/technology/why-isnt-vivaldi-browser-open-source/
Still far from open source or free software, but better than most people would think. I guess you would also have to trust them that it really is just the UI.