open water swims
You don't need Android File Manager to use Garmin Express. You need Android File Manager if you want to access the file structure on your device.
I think the issue with the music might be something to do with DRM, but I might be wrong. There are a number of posts dotted throughout this forum about music and the 5+.
The latest public release software is 6.0. this was released in early December - https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-5-5s-plus/1429464-software-version-6-00-now-available. If you cannot update to that then you need to find out whether you have a ROW (Rest of the World) or APAC (Asia Pacific) device. That might well depend on where you bought it. Since you live in the US chances are you do have an ROW device, but there have been instances where APAC devices have been purchased in the US. Typically APAC lags ROW in software by a couple of months or so. Not sure how you can check that on the 5+. Someone else might chip in here.
rtperna - I have to ask - how are you destroying the watches :) - I have had a 935 with no issues running roads and trails and swimming open water sometimes in large rough groups. I actually find that I am noticeably knocking my 5+ against things much more often ( I think due to the greater thickness and weight) but it is not showing signs of damage yet after about 3 months.