I had the same problem (trying to pair, but my garmin kept displaying 'connecting' for a while, and then said it failed to connect):
* I reset my garmin to default settings
* I unpaired the device…
This resolved my bluetooth issue after updating my iPhone to the new iOs 13 version. Thanks so much for posting!
I had the same problem (trying to pair, but my garmin kept displaying 'connecting' for a while, and then said it failed to connect):
* I reset my garmin to default settings
* I unpaired the device from the bluetooth on my mobile phone
* I uninstalled Garmin Connect app
* I re-installed it
* (1) from Steetings->Blootooth I clicked Pair Mobile Device, and while it was showing "Ready to pair" on my garmin: (2) From the garmin Connect app I clicked the icon of the device, chose Forerunner 235 and (not remember exactly how) clicked something like 'pair device'.
Not sure all the steps are necessary, but this what worked for me.