The standard advice here has not changed really. For a plain Jira core installation, you can consider a "component" to be a "sub-project". The other thing to look at maybe categorising your projects, so that they're grouped together as "sub-projects" themselves.
In fact, there isn't really any concept of a "sub-project" - a big question has always been "what would you expect a sub-project to do, that you can't already do by having a simple project?"
If you have Jira Software, you've got another option - the Epic can be used to gather together issues across many projects.
And then if you get things like Structure or Advanced Roadmaps, you can have more options about grouping things together.
To add a little to what @Nic Brough _Adaptavist_ said with respect to Advanced Roadmaps. We have used an approach where we create additional hierarchy levels above epic and then associate those with issue types only available in a project designed to cross-cut multiple other projects (these might be what you'd consider your sub-projects) and then use Advanced Roadmaps to build a cross-product plan.
For example we might have an initiative like "GDPR compliance" that exists in our overarching project and then have epics in each sub-project for different products or offerings that have the initiative as it's parent.
This approach means that each product can have it's own plan that include the issues from the overarching project as well as from it's own project without bringing in all of the work products issues and we can create a plan across all projects that only goes down to the epic level across all issues (to reduce the size of the plan). There are some limitations to this approach, but depending on your specific use case it might meet your needs.
However, you would need to upgrade to a Jira Premium license to get Advanced Roadmaps.
We had the same "problem" and so we started using Epics as Nic said.
Since we needed more debt we added issue type "project" and added custom fields to it like Project Lead(user picker), Project Members(multiple user picker), deadline. Project (issue type) is below epic)
And we use BigGantt so you can see clearly who the "project lead" is who members are, you can plan the time it's great.
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