In a recent communication, Amazon has alerted Kindle users about significant changes set to take effect from next month. The notification pertains to the phasing out of support for sending MOBI (.mobi, .azw, .prc) files through the “Send to Kindle” feature, starting November 1, 2023. This change, as News18 pointed out, specifically impacts users attempting to send MOBI files via email and Kindle apps on iOS, Android, Windows, and Mac.
Libra 2 and Clara 2E both have internal micro sd, from the currently available models. You have to remove the back cover of the reader to replace them. Wiki lists all features of all readers, check the “Storage” column: https://en.wikipedia.org/wiki/Kobo_eReader