2020 Bishop Dual Sport Oct 9-11th
Let VCMC help you $donate$ to the OHV cause:
I installed a Sandisk microSDXC 64GB Ultra into my unit. It was recognized by the SW on my computer, and I could load Topo 24K maps (using MapInstall) and upload custom maps to the SD card. I found however that the GPSMAP 64st could not access anything that was loaded onto the 64GiB SD card. I contacted Garmin support, and they told me that the outdoor handhelds have problems with ExFat-formatted SD cards. The SD industry has adopted ExFat for cards larger then 32GiB, so 64GiB cards are formatted using ExFat and cannot be used reliably by a Garmin GPSMAP 64st. After a quick trip to Staples to get a 32GiB microSD (which is formatted as FAT32), I soon had maps installed onto the 32GiB card and most importantly accessible by the 64st.
I followed this link to solve my formatting problem.