The public option is literally in Bernie's M4A bill.Harris and Booker both co-sponsored Bernie's M4A bill, but then backtracked on the main component of that bill within ~24 hours. Right now they are both backing 3 different healthcare bills each, one of which is barely different from the current system. I knew it was too good to be true.
https://news.yahoo.com/kamala-harris-backtracks-vowing-eliminate-131505611.html
https://www.vox.com/policy-and-politics/2019/2/1/18207383/cory-booker-2020-medicare-for-all
The reason you consider this "too good to be true" is that you've repeatedly attacked Harris in prior threads, but it's not a surprise someone dumping on US candidates from the UK wouldn't be aware of that.