You can export OSM XYT Tiles background map as raster file: right click on the OpenStreetMap layer and select Export / Save as... to save a copy of the background tiled map as raster file. Be sure to define the extent and resolution of the raster.
However, you don't write why you need to do so, what you ultimately want to do with this raster. Maybe there are better ways to achieve that.
OSM XYZ Tiles map (brighter, in the background), and exported raster file (darker, in the middle):
