The Descent Mk2i synchronizes and updates with Garmin Express for Mac 7.2.0.0 without a problem.
The storage is not mounted on my iMac as Descent Mk1 does.
Hence neither Garmin MapInstall 4.3.4 nor Garmin MapManager recognize Mk2i.
I would like to install OSM Maps on it.
Any pointers?
N.B.
The USB mode of Mk2i is currently set to MTP mode and Garmin Express does not work if I set to the USB mode to the only other option, Garmin mode.
The USB mode of Mk1 is set to Mass Storage mode.
Try Android File Transfer
https://www.android.com/filetransfer/
I use this with my Fenix 6X in MTP Mode to be able to copy files directly to the watch file system which will appear on my Mac desktop as…
Great, glad I could be of help.
Theres a few sites to get maps from.
I've used ones from this site and just copy them on to the watch manually.
I mounted Descent Mk2i using the Android File Transfer as suggested by Maruzko above.
I have found that the old way of copying map files works. It took much longer than I have expected. Maybe the files are much bigger but they works. 
