unfortunately I am not so familiar with QGIS that I can give you a concrete solution or hint about an error in your workflow.
But:
Is there any reason why you have a quite old QGIS version in use? Using a more recent version can solve some errors, maybe.
then,
are you aware of importing raw OSM data via the QuickOSM plugin? Did you ever used that inside QGIS?
Maybe it is a matter of missing or wrong map paint style?
Due to lack of time I cannot try to reproduce your workflow, but maybe via a general web search about “import OSM data QGIS” you can find some hints,
Keep in mind that OSM data format isn’t like all the formats GIS packages are familiar with (eg. shapefile).
There are nodes, ways and (few) relations. The only means to tell that a way is a polygon vs a line is to (besides requirement of being closed) check tagging.
When you import into QGIS you have to define a layer. Like: “import all closed lines with building=* tag to an area type layer, and import some keys into attribute table columns”. You see dots because you didn’t define what you want and it just imported all the nodes into point type layer.