I guess you can use Attribute Manager for this. Create new Output Attribute value as "single attribute sahpe" and add in "Attribute Value" like below.

@Value(shape{0}) @Value(shape{1}) @Value(shape{2})

I hope it will work.

In a dynamic scenario, where you don't know the names of the lists, I can't think of a way to do this other than via scripting.

Something along the lines of

import fme
import fmeobjects
import re

def processFeature(feature):
    # get all the unique list names
    rootNames =set()
    attrList= feature.getAllAttributeNames()
    for attr in attrList:
        list = re.search('(.*){o0-9]*}(.*)', attr)
        if list:
            listName = list.group(1)+"{}"+list.group(2)
            rootNames.add(listName)
   
    #get the values for each unique list and concatenate them
    for listAttr in rootNames:
        listVal = feature.getAttribute(listAttr)
        concatVal = ','.join(listVal)
        newAttr = listAttr.replace('{}','')
        
        #add the attribute to the feature
        feature.setAttribute(newAttr, concatVal)
 

There is an existing enhancement request for this behaviour. It's PR#15122 - the low number tells you how old that request is. Sadly I don't think there have been a lot of requests. But I will add a link to this thread and see if I can increase the priority.

@jdh

Great - your python script does the trick. Thanks a lot!!!!!

Thanks to the others as well-

Arrived here this morning after thinking there must be an alternative to many listconcatenators or a python script but seems not, I thought it was just lack of coffee and my brain not being awake!