In addition to Opire for short-term opportunities (aka bounties), there is Algora.
In fact, there are a few of such bounty platforms in my notes, but Algora seems to be the one with the most traction: in terms to new tasks to work on and the bounty amounts being competitively priced.
Here’s an example of a 2-3 month bounty offering up to $20,000 on Algora, for someone with React Native skills: https://github.com/BasedHardware/omi/issues/1944