Using Avenza PDF on Monterra - SD card map issues

I have been using this app on other Android devices. While this being a Garmin, I may not use as much, I would still like the ability to use it occassionally. That said, it's very difficult to add maps from the SD card. The standard way the app should work is to Import map "From SD card" as one of 3 options. The Monterra doesn't give this option. It shows only Import map "From Device Storage" which doesn't include the SD card, so there is no easy way to copy maps from the SD card. I loaded a file explorer app and I can click on the map there and it will open in Avenza. However, it appears that after one map it will hang and I have to shut the device off to get it to load another map this way. Sure wish the app worked like it should on this device. Maybe this is due to the older version of Android? Maybe this will get updated someday?