Supernote has links, as does Boox. There is a specific Star based system for Supernote but I never quite got the hang of that, but I use the linking features extensively to link to pages of PDFs for more extended notes about them, and to serve as a sort of directory / tree structure for notes and subjects. I keep my notes structure fairly flat for that reason, there aren’t many folders.

I’d’ve shelled out $800 first thing this morning for an RM Pro if they added linking across the system.