This is very possible and Bubble does support loops. I have pasted a link below that explains recursive workflows, but a summary of your solution is as follows:
(A friendly word that recursive workflows can take a bit to get your head around, but once you do they are quite simple to replicate and extremely powerful. And should always be used vs doing something on a list).
Create a backend WF end point called something like “CreateNewBThing”.
Within CreateNewBThing you will specify the keys (new world speak for variables) that you will pass to CreateNewBThing. Reference first image below.
Then add an action to do some action like “Create a new thing”. Reference step 1 in second image below. In my case I do a number of steps so I have a separate backend WF end point for all those steps, but I believe your case would be a simple single step to create the new B thing.
Then add an action to call CreateNewBThing (itself and therefore the loop). Reference step 2 in second image below. Within this action you will specify 2 aspects of the loop: Firstly what the end step is (only when) and how to increment. My increment is based on MatchNumMin and finds the next matchNumber that meets the criteria specified and is bigger than the current (Min) number. Yours would be a much simpler counter or the like.
Reference Image one - Back End Workflow end point:
Reference Image two:
