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.
To get the extent of a layer, simply click Calculate from Layer... in the Extent section of the dialog window (...
You must provide all required parameters. Parameter values must have proper type, e.g. setting tile size tw=100 is correct, but tw=100.0 will not work.
'rasters.global_dem', -- source raster table
'rast', -- raster column