In macOS Tahoe, Mail inserts images directly into the message at the current insertion point.
Apple’s current Mail documentation also provides the option Mail >> Edit >> Attachments >> Always Insert Attachments at End of Message, but this controls where the attachment is placed
Apple does not document any setting that controls whether the cursor is left before or after an inserted image. Apple: Send attachments in Mail on Mac
Therefore, there is currently no Apple-documented preference for restoring the previous behaviour in which the cursor automatically moved to the right of an inserted image.
Changing Always Insert Attachments at End of Message will affect attachment placement, but Apple does not indicate that it changes the cursor position.
Apple’s current Mail User Guide for macOS Tahoe likewise contains no setting for the insertion-point behaviour after inserting an image.
So, based on Apple’s published documentation, there is presently no supported setting in Mail to restore the old cursor behaviour.
If the user believes that this bears the attention of Apple for a possible feature addition
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However, at this late stage in the development of macOS 26 Tahoe, it is doubtful that most of Apple’s resources are likely focused on the next version of macOS 27 Golden Gate.