That looks like an old version of Convex.jl. What version do you have? Try
using Pkg
Pkg.add(name="Convex", version="0.14.5")
to get the latest (or hopefully get an informative error message about what packages are holding it back, if you can’t get the latest).
Convex definitely should still be working and every release is tested with a large test suite of problems by CI.