SUMMARY *** launching a connection from the PC to the smartphone fails. launching a connection from the smartphone to the PC succeeds. *** STEPS TO REPRODUCE 1. at the PC, click the "connect" button, this fails. 2. at the smartphone type on the name of the PC, this succeeds. 3. SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: (available in About System) KDE Plasma Version: 5.25.5 KDE Frameworks Version: 5.98 Qt Version: 5.15.5 KDE Gears 22.08.1 Bluez 5.65 ADDITIONAL INFORMATION the smartphone is a Bluetooth 4.0 one. I did the same experiment with another Bluetooth 4.0 smartphone. Same result. In the past, this was working. I was using a Bluetooth 4.0 USB dongle. Today I use a Bluetooth 5.2 PCI card EDUP LOVE ep-9651GS (intel AX210).
Most likely this is an issue with bluez/the kernel, not Plasma. All Plasma does it tell bluez to connect to a given device, there isn't really any room to do something wrong there. Please report this to https://bugzilla.kernel.org/buglist.cgi?component=Bluetooth&product=Drivers&resolution=---