Thank you for your replies.
My first Garmin gps was a Montana 650, which after the first year of using it; died. Garmin replaced it, that unit never worked from day 1, and again Garmin replaced it. That one worked for a summer and also died. Again Garmin replaced it, and yet again it died. After having 5 of them I decided to stick to less expensive units, I now buy *new* used items. Above gps I used with basecamp and windows computer. basecamp was finicky but I was able to mount and unmount custom maps.
Next gps was a Garmin nuvi 2597. Took it apart, filled and sealed it up with silicone to make it (as much as I can) water resistant to be mounted on an unfaired motorcycle (used it all over s.e. Asia). to which it worked amazingly well (it still works). loaded custom google street maps (also OSM street maps) via the usb power/ data cord, as the micro sd card was siliconed in place. Above gps I used with Garmin express and linux (elementary os) computer. mounting and unmounting custom gpx maps.
The 2597 was/ is a decent gps, but it the processor is a bit slow to deal with as is the screen quality/ size. so I upgraded to the drivesmart 65. the plan is to also fill it with silicone and to be mounted out in the elements on a motorcycle. removing the sd card would have been an easy solution but in my case not really valid.
I used the drivesmart last summer, easily loading (and unloading) custom google street maps converting the KML file to GPX
(here), cut & paste directly into the gpx folder on the drivesmart via the supplied Garmin cord and elementary os.
have upgraded to a M1 13 MacBook which only has two USB-C ports, and the drivesmart cable uses USB-A, hence the dongle. but I found it interesting that the mbp was able to see the thumb drive, but not the gps. which made me wonder if they were simply not speaking the same language.
I tried connecting the dongle up to my Samsung tablet, and the thumb drive via one of the USB-A ports, it worked. I then tried the drivesmart, the tablet could see it, and acknowledge that it was plugged in but unable to see any folders. so maybe it was less of a Garmin issue and more of a language issue.
I then did some reading on google to see if I could find anything, and I found this
page. after cross referencing the suggested MTP issues and some more googling for their idea of a solution, I downloaded the Android File Transfer, and gave it a try. The drag and drop to instal an application on a MacBook seems bizarrely weird, if it weren't for the wife I wouldn't have gotten past that part.
In the end I got it to work, I was able to access the gpx folder on the drivesmart via the Android File Transfer pop-up window, to manually load and delete my custom gpx files via the supplied Garmin cable and using the anker usb dongle. it does not show up in the Disk Utility.
Once again, thank you for your thoughts and ideas