If you are building your own Qt 5 then you should see if the notes about enabling the Win32 API apply to you.
Qt 5.14 adds a native Win32 port supporting Classic Bluetooth on Windows 7 or newer, and Bluetooth LE on Windows 8 or newer. It must be enabled at build time by configuration option -native-win32-bluetooth.
BT LE did have a restriction under the Win32 API that may also at play:
Note: The Received Signal Strength Indicator (RSSI), as well as the Manufacturer Specific Data advertised by Bluetooth LE devices are not supported by the Win32 backend. Also, it is only possible to find devices that have been previously paired through Windows Settings.
Qt 6.2 reintroduced Qt Bluetooth after it was ported from Qt 5. In that process, "Win32 backend was removed. As consequence there is no more QtBluetooth with MinGW." This may have changed the default BT API used and explain a changed behaviour. Cannot say for sure without reading the actual code.