I installed QGIS 3.0 (standalone 64 bit installer) and added the standard XYX Tile layer 'OpenStreetMap' that was part of the install. It loads fine except the text is too small to see. Not sure if the small text size is caused by my high DPI (3200x1900) screen resolution? I also tried: 1. Adding my own XYZ Tile layer (instructions used were from here: http://www.xyht.com/spatial-itgis/using-openstreetmap-basemaps-qgis-3-0/) but the result was the same. 2. Adding a Google Maps layer (instructions used: http://www.geodose.com/2018/03/how-to-add-google-maps-layer-QGIS-3.html) and again, the text is too small to be usable.
Both OSM and Google Maps render the text at a readable size in my web browser (Chrome) so the issue is with QGIS 3.0 and not OSM or Google Maps.
Update - 1 April
I've had some suggestions to use high resolution (retina tiles). I tried the suggested links but the text in the maps were still too small. The links no longer work (it appears the services are no longer available) but I'm also not certain I used the correct URL either.
Can someone provide me with a URL to a working high resolution Open Street Map service.