Any suggestion on how to filter for ARM generated entries only? We are unable to use Memo:“Rev Rec source” and “rev rec destination” due to the old rev rec module

Try Created From:Type? It's not visible on JEs, but I'm pretty sure it's still populated. It's definitely populated on legacy Rev Rec entries; I'm less sure about ARM entries. Might be able to do it with Created From: Type=SO/Invoice/Rev Arrangement. Whatever transaction type it populates, I don't remember. If it populates. I haven't dealt with ARM for a couple years so that could have changed. But worth a shot!

I would use system notes for that, system rev rec journals have Context = Bulk Processing