This has more to do with macOS Sequoia (at least) and connectivity issues with (at least) the eTrex 22x & 32x devices.
Since there are no dedicated forums to properly judge where this should be posted, I picked this forum.
This is also more of a "How I got it to work" post than requesting help... but if someone has an actual solution for this issue (that seems to be on Apple's end after all my testing), please feel free to let us know.
I hope this will help someone out who is also having this rather annoying issue.
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Unit: eTrex 22x -or- 32x (I have tried both and exchanged for different units to rule out a faulty unit)
Unit software v2.90 (I also tried v2.80 with the unit directly out of the box)
Using an M1 MacBook Air 2020 -or- an M2 MacBook Air 2022, both under macOS Sequoia, here is the problem as far as removable media and the eTrex goes:
If a microSD card is NOT present in the unit, connecting it to either MacBook will properly mount the internal GARMIN drive just fine, with no issues.
If a microSD card IS present in the unit, both drives will NOT mount properly and the Mac throws two identical error messages (one for each drive): "The disk you attached was not readable by this computer, Eject, Ignore, Initialize". Choosing Eject will of course eject the drives, Ignore does nothing and Initialize simply opens Disk Utility where one can do Disk Utility-type stuff to them but NO means to manually mount them.
The main problem comes with when you want to update the maps on the unit with Garmin Express. The 8GB of internal storage is not large enough to load the larger mapset so the microSD card is required. If only the Garmin drive is present, the maps will not update telling you that the internal storage is too full for the update & for you to insert a microSD card for the update. If one inserts the microSD card, the drives will of course not mount because of the issue.
The USB cables used (3 different cables, all were Garmin supplied) was ruled out. Various USB-A to USB-C adapters were used, as well as a powered HUB and even a dedicated USB-C to miniUSB cable, with no adapter being used (these all turned out to be just fine as well).
The microSD cards tested were all 32GB or under in size and were formatted under FAT32 and work fine in the unit and mount properly with the older MacBook as well as two different Windows PCs, as well as three different iPads (as below).
The problem does NOT exist using two different Windows 10 desktop PC's or a MacBook Pro (Late 2011 running macOS High Sierra using the same USB cables.
This problem also does NOT exist if I plug the eTrex unit into my iPad mini 6, or iPad Air M1 & M2's USB-C port using a USB-A to USB-C adapter. The iPads will easily recognize and mount the drives using the same cables/adapters tested with the MacBooks.
Here's what I eventually did to get the both drives to mount under the newer MacBooks & newer macOS:
1. Log out of the current MacBook user account (stay at the login screen)
2. Power on the eTrex GPS
3. Plug in the USB cable (still at the login screen)
4. Wait a minute to a minute and a half
5. Login to the MacBook
The drives are then both mounted and operate normally. Periodically, the GARMIN drive will not auto-mount and I need to use macOS's Disk Utility to manually mount the drive.
Note that If I eject the drives, they will again NOT mount if plugged back in under the same session and the process above needs to be repeated.
I chatted with support a few weeks and told them of this issue. The support person did mention that Apple has changed the way macOS handles removable media over the years by quite a bit and that it sounded like macOS (at least in this case) seems to not like piggy-backed drives.
