right-sidebar-blocks and discourse-tc-bars are both using the Ember resolver to lookup components by name. Right now that works, and is not deprecated.
In .hbs it’s done like {{component "some-name"}}, and in (g)js it can be done like resolveRegistration("component:some-name").
But if we’re talking long-term here, then we should be aiming to avoid looking up components on the Ember resolver. Once we eventually enable Embroider’s “static invokables” flag, the resolver will be empty.
This is the direction I think we need to take for right-sidebar-blocks, and other similar cross-theme/plugin component sharing: