Linking records between them is the bulk of what most UIs are supposed to do. Yet, I feel like the native reference selector and reference set selector have been stuck in the 2000s in terms of design and functionality.
Design-wise, the marketplace multiselect alternatives prove that there doesn’t necessarily need to be a difference in the way single-select and multi-select are displayed.
In terms of features, I feel like Autocomplete, Force refresh (myself and others) and the ability to add a new record from the dropdown are must-have functionalities for a modern drop-down.
Unfortunately, the marketplace doesn’t provide currently with a close-to-perfect solution, as summarized in the following link https://docs.google.com/spreadsheets/d/13kXmdYnOIpPcawFiDQ_xA-YMEBJ5lNlFjt9RXxL16Pw/edit?usp=sharing (feel free to update/enrich).