There is some relevant functionality, but it is probably not what you had in mind, and it is not (yet) very convenient to use.
There are two approaches that you can use, both of which rely on the unique identifier that Bitwarden assigns to each vault item.
Deep Link to Web Vault Item:
When you open an item in the Web Vault, the URL in the address bar can be copied and used later to access that item (if you are logged in). For example, if you store that URL in a related vault item, then you can copy and paste that URL into the browser address bar, and hit enter; this will take you directly to the linked item. This works because the URL will be of the form https://vault.bitwarden.com/#/vault?itemId=xxxxxxxx-yyyy-yyyy-yyyy-yyyyyyyyyyyy, where the string that follows itemId= is the unique item identifier. For more information, see Help article on linking.
Search for “Short” ID:
If you know the item identifier of the item you wish to link, then you can use the first 8 characters of the ID as a search term. The first 8 characters of the unique item identifier are referred to as the “Short ID” (in the web vault URL example above, xxxxxxxx is the “Short ID”). Thus, you can store the short IDs for related items in the Notes section or in custom fields and then copy and paste those 8-character strings into the search bar. If you need better specificity in the search results, you can used an advanced search expression of the form >shortid:xxxxxxxx
You can also obtain the item identifier from the browser extension. The easiest way is to open the vault item of interest, then pop out the extension into a floating window, right-click the window and select “View page source”, and examine the URL in the address bar of the window that is opened (the URL starts with view-source:chrome-extension://, and contains a query term ?cipherId= that is followed by the item ID).
Some of this would be easier to use if progress is made on this related feature request:
I would encourage you to describe in greater detail your vision for what the linking function you have requested would look like, and how the user would interact with it.