Whether or not your Deployments are queued depends on the amount of Concurrent Builds you have available. Personal accounts are limited to 1 Concurrent Build, while teams can customize the amount on the "Billing" page in the team settings.
Learn more about how to adjust your Concurrent Builds here.
After having set up your monorepo as described above, each of the directories will be a separate Vercel project, and therefore be available on a separate domain.
If you'd like to host multiple projects under a single domain, you can create a new project, assign the domain in the project settings, and proxy requests to the other upstream projects. The proxy can be implemented using a vercel.json file with the rewrites property, where each source is the path under the main domain and each destination is the upstream project domain.
Pushing a commit to a Git repository that is connected with multiple Vercel projects will result in multiple Deployments being created and built in parallel for each.
To access source files outside the Root Directory (which enables Yarn & Lerna Workspaces), enable the "Include source files outside of the Root Directory in the Build Step" option in the Root Directory section within the project settings.
Vercel projects created after August 27th 2020 23:50 UTC have this option enabled by default.
If you're using Vercel CLI, at least version 20.1.0 is required.
Because Vercel CLI only allows for linking a single Vercel project, you currently need to clone your Git repository multiple times (once per directory you want to deploy or develop) and then link a project for each.
Use Vercel CLI 20.1.0 or later to ensure you can take advantage of the option for accessing source files outside the Root Directory (mentioned in a section above).