Upwork can be really great, but most people use it wrong.

Don't wait for the good developers to apply, invite them proactively. 95% of the developers applying themselves are sadly the bottom barrel. First weed out from their profil history if they know what they are doing. Only work with people that have 100% Jobsuccess with relevant projects and have the "Top Rated" Badge. Then do a small test project with them or a free consultation call to check for details, how good their english is and cultural fit.

I have both hired myself and got hired on very successful projects (e.g. build an MVP for a startup in a month that led them to secure a funding round) this way. In case anyone wants to see my profile https://www.upwork.com/fl/tobiasheidingsfeld