it's nice to have an explanation. for me, I just wanted to quickly make them. Googling led to ad covered sites and "register to use" site. Found a few on GitHub but they had other issues so threw together my own using a well designed library I'd used before. took about 15 minutes
https://greggman.github.io/qr-code/
might add more options but in truth I don't think most users need the options