Hi Noons11, my comment about customizing the toolbar was in response to a side question not related to the original question of flagging emails.
If your goal is to flag emails, please see my other replies, in particular those at the beginning of this thread. The "curved arrow" icon is confusing, I know. The one you sere at the top of an email is to reply to the email. The one at the very bottom of an email (scroll an email all the way down to see it) is for accessing other functionalities, in particular the one that flags the email. (I show a screenshot of this special "curved arrow" icon in one of my replies.)
I also stated that, for reasons I ignore, some users cannot see this icon. I can't think of any reason why this should be. My 2 iPads (iPad Pro M1 and iPad Air 3) on iPadOS 26.2 show the icon.