Of course it would be good if those of us using Macs were actually able to install the firmware... same issue as for the UT800 update here: https://forums.garmin.com/forum/garmin-express/garmin-express-mac/1270820-garmin-express-crashes-when-updating-varia-bike-radar
I am currently experiencing a similar issue with my RTL515. I believe this poses a significant safety concern, and it is imperative for Garmin to address this matter promptly. The potential consequences in terms of image damage could be substantial if an incident were to occur. If this problem is not rectified, I am contemplating discontinuing my purchase of Garmin products.