Creating an environment to use specific versions of packages, Julia uses most current anyway

[hendri54]

You may be running into stacked environments:

https://docs.julialang.org/en/v1/manual/code-loading/#Environment-stacks-1

Shared environments

I recently learned about “shared environments”, aka the default v1.3 environment. It’s quite a revelation, but I don’t understand how it works. Suppose I have Package A which depends on B@v1.0.0, and is compatible with no other version of B. A is in the shared environment’s Project.toml. Environment E, which has package C in its Project.toml. C depends on B@v2.0.0 (compatible with no other version). When I am in E and I using A, which version of B is loaded?

If you previously activated an environment that (even indirectly) loaded the newer version of JuMP, the Manifest entry no longer matters.