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Calibre recognises the SD card and I can then load books as if the Kobo was connected. I take the mini SD card out of the Kobo and insert it into the Lightning hub (I have one of those hubs with multi ports). I have found a partial work around that enables me to load books onto the Kobo. Apple support are no help and really don't want to know about it and I haven't heard back from Kobo. It would appear that it is the M1 chip causing the problem. You have done basically what I have done and with the same result. Meanwhile all the old tricks like resetting the SMC are not valid on these newer computers. The only card that I can reliably use is a UHS-2 Card from sandisk (32GB, 280mbps). Same for 4 other 32GB cards from sandisk (also UHS-1).
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But I'm not sure they have an M1 computer to test on. My SanDisk Extreme Pro SD Card with 256GB and 95Mbps (UHS-1) is so unbearably slow but works fine with an external reader on the same MacBook. I have been in contact with Kobo support and they have no idea why it's not working. So it was the switch to the M1-chipped computer that started the problem. nonda USB C to SD Card Reader, SD/MicroSD to USB C Card Reader Adapter Thunderbolt 3 Compatible with iPad Pro 2020/2019, MacBook Pro 2019, MacBook Air 2020, Galaxy S10/S9, Surface Book 2 and More 4. This exact same H2O was working perfectly on my previous laptop, a 2013 MacBook Pro also running Big Sur.
MY MACBOOK PRO SD CARD READER WORKS SOMETIMES INSTALL
Even did a complete clean install of Big Sur, still no dice. Have tried everything from factory resets, many different cables and adapters, a direct USB-C to micro-USB cable, booting into safe mode, and creating test user accounts. Can't connect my H2O to my new M1 MacBook Air w/ Big Sur no matter what I do. Wanted to chime in that I am having the same problem.
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