Setting of the osm plugin (possible other plugins too) for a map cause freeze of the ui relative to the cache size (size of the existing images in cache directory). I did some experiments with code:

    Plugin {
        id: osmPlugin
        name: "osm"

        PluginParameter {
            name: "osm.mapping.cache.disk.cost_strategy";
            value: "bytesize"
        }
        PluginParameter {
            name: "osm.mapping.cache.disk.size";
            value: 1073741824
        }
    }

    Map {
        id: map
        anchors.fill: parent
        center: QtPositioning.coordinate(59.91, 10.75)
        zoomLevel: 10
    }

    Timer {
        running: true
        interval: 500
        onTriggered: {
            console.time("Time")
            map.plugin = osmPlugin
            console.timeEnd("Time")
        }
    }

Results are:

Ich have noticed that earlier initialization of the OpenSSL (for example calling of the QSslSocket::supportsSsl()) on application start maked the times about 400 ms shortly. Despite of this the time it takes to initialize the plugin in the map leads to freeze of the ui (even when cache is empty).

I suppose that growing of the time relative to size of the cache is associated with indexing of the tiles. Maybe it is possible to be done asynchronously.