What happened to "show related messages" in iOS 13

is it me, or has “show related messages” disappeared from the more menu after swiping left on an email message? i haven’t seen any mention of this anywhere, and really miss it. thanks

I think what you are looking for changed as opposed to disappeared. In Settings -> Mail do you have the “Threading” settings set to your satisfaction? I have “Organize by Thread” and “Complete Threads” both checked. When I am looking at a specific email conversation in the Mail App if I scroll down I see the entire conversation and if I scroll up I see each separate message.