The whole social aspect of Venmo is one of the stupidest things to have ever been created. I use Venmo because it's the most widely used platform, but all of my transactions are private.
Do people even scroll through the public feed of their friends? Why does anyone care that their friend paid another friend (who they likely don't even know) $10 for a burger and fries? So fucking dumb.
"Lockup" is an investment term. When a company has an IPO (Initial Public Offering, which is the day they become publically available for stock trades), the big shareholders and company employees who are invested ahead of the IPO are "locked" from selling their shares for a certain number of days. This isn't required, but most companies having an IPO end up having a lockup period set as well.
In regards to this headline, it just means that the initial investors and big shareholders are now free to sell their shares, which they are apparently doing in droves!