To the point of filtering in org-roam, I think it needs to be addressed differently depending on the use case and workflow of the user. The function thankfully provided by @nobiot comes in handy for (on-the-fly filtering) that requires alternating node finding scheme in one session without being strongly committed to a specific scheme in mind, the user would like to have all subdirs at disposal and no intention to filter some indefinitely.
But for another use case, where the user wants to stick to a fixed PRESET subset of subdirs for a number of days on domain A without bothering any of B and for another number of days on domain B without bothering any of A , I guess, a different setup would be necessary.
One suggestion as pointed above, passing a subset of subdirs to a variable (scheme), and it has as many subdirs as the user want to process for each domain (domain A: subdirA, subdirB, subdirC; domain B subdirD, subdirE). The variable must be customizable so that user will set the variable to one of the schemes with its associated subdirs once without bothering to input different schemes and their associated subdirs each time each session to find the relative nodes, this will save many keystrokes in my opinion.
On that day when working on domain B is required, the user can again change the value of that variable to set the scheme value to B and its associated subdirs. I think this mechanism is effortless and more convenient to the org-roam-busy user in this case.