The SD card reader is one of three ports that returned to both MacBook Pro 2021 models after being removed in 2016, along with HDMI 2.0 and Magsif ports. The port supports the UHS-II standard in the new 14- and 16-inch MacBook Pro models. This standard could theoretically provide read and write speeds of up to 312 MB / s; But the new MacBook Pro supports data transfer speeds of up to 250 MB / s for UHS-II based cards and up to 90 MB / s for UHS-I based cards.
However, the new port seems to be causing problems for users of Apple’s new notebooks. For example, some users report that the device can access SD cards; But the transfer rate is abnormally slower than expected. Other users report that the device may sometimes not be able to identify the connected card. One user says about this:
In some cases, the device successfully detects the card, and in other cases, it can not do so. All Ultra Sandisk cards, both XC and HC, formatted on my camera have this problem. I tried to re-format them with MacBook Pro and it did not seem to make a difference. All my cards work properly on the other three USB card readers.
It is said that users are usually faced with three scenarios: In some cases, when trying to use the SD card, only the error message is displayed and sometimes the finder does not work properly and in the last scenario, it takes minutes for the SD card to be identified and accessed.
In general, it is not yet clear where this problem comes from; But it does not seem to be related to the content format. The report states that Apple support staff is aware of this issue and is considering resolving the issue with future software updates. Apparently, users who received a new MacBook from Apple after announcing the problem did not see the other items mentioned.
One user says that Apple has fixed this problem in the beta version of macOS Monterey 12.1; But someone else at Reddit claims that this issue has not been resolved in the latest beta; Therefore, the accuracy of any of them can not be confirmed or denied.