Please can soemone kindly help me on a required filter

[gdhm]

I always use Update (left to Right)
I have 4 filter pairs backing up to a Flash Drive

My Flash Drive was near its capacity so I decided to reduce my include sub folders by a few.

the pair is:
O:\FAILSAFE BACKUPS Update> [SD 32GB USB3 Important]\FAILSAFE BACKUPS

and I had a few sub folders in the central Filter section for that pair in the INCLUDE section
e.g \(KEEP) WLM *\

I, probably stupidly, assumed that when I ran compare that the no longer included sub folders and files would appear on the right side (which after I ran "Synchronise" would be there for me to delete.
I assume the reason they were not shown is because FFS is doing exactly what I requested and only compared the reduced remaining folders (and IGNORED all others on left (source) and right (destination). Seems logical thinking about it.

So I had to go and manually delete the no longer required sub folders that existed in the destination Flash drive via Windows Explorer.

OK My question, dumb as it may be:
Is there a filtering syntax/mask I can use that I can use with "Update" Synchronise that will compare the INCLUDED sub folders/files and ALSO show any sub folders in the RIGHT side (destination) FAILSAFE BACKUPS that are not on the INCLUDE Sub folders list for updating (so I can view and delete those no longer wanted).

Sorry if this is just not a normal requirement, or there is a serious risk I have not considered by trying to do this. I ask because occasionally I need to cull stuff on my Flash Drives and what I wish would make things a little easier to identify than searching for them manually via Windows Explorer.

Many thanks all.

[Plerry]

If I understand correctly what you want, it is (almost) already in the FFS tool.
If you run a compare between the indicated locations based on the Update method, you will see a couple of buttons behind "Select view:" at the center below the left and right folder/file listing.
Normally for an Update sync these are:
"=" : left and right are equal
"-" : files that won't be copied
"=>+" : files that will be created on the right side
"=>" : files that will be overwritten at the right side
If you now click those buttons such that only the "-"-files are show, that should be your list of files existing on the right side, but no longer existing on the left side. By in the right window/list right-clicking on a file or folder, you can (amongst others) select to delete that file or the folder ...

However, if you have excluded items via the exclude filter, those will not show up in that list.
So, what you might do is:
Save your sync settings e.g. as MyActiveSync.ffs_gui
Remove the exclusions of all specific folders from your exclude filter, and store those sync settings e.g. as MyActiveSyncCleanup.ffs_gui.
If you now run the latter, it will show you under "-" all files and folders existing on the right but no longer existing on the left and as decribed, you can now delete those.
But, if you want to delete all that is present right but no longer left, you might just as well use the Mirror method.

[gdhm]

Thanks ever so much Plerry :) I will do that.

(Hmmm.... seems I need to spellcheck my Topic Title as well as my posts content)