Running M65Connect 5-JUL-23 Windows Build the SD Card Manager always lists as Internal with no way to pick internal or external (only internal is available).
It appears that when an external card is in, that card shows contents and is listed as internal and if there is no external SD card the behaviour appears correct. i.e. the Internal card is listed and the dropdown shows internal.
Not sure if this is a bug or just normal behavior with the internal card being replaced by the external one when it is present.