I've managed to link QGIS3 to Google Earth via XYZ tiles. I would like to convert the Google Earth map shown to a GeoTIFF raster (to save on memory?). I try and export the Google Earth layer to a GeoTIFF raster and notice a the bottom of the screen I have to choose extent - assume I click mapview extent, because the original Google Earth files must be large? And then I need to select the resolution? This is the bit where I am struggling, because on the layout composer canvas I want to produce a map at A0 size with a scale of 1:5000, and if this works, at 1:1250. A previous post I've found noted that the resolution units are metres per pixel - so how do I choose an appropriate resolution, noting the printing specifications of the map to be produced? Also a previous post queried whether this method of exporting Google Earth data is actually allowed?
The image resolution of your exported geotiff won't affect the scale of the map you produce with it. When you produce a map in the print composer, QGIS will automatically zoom in or out on the image to the same scale as the map (that's the point of making it a georeferenced image rather than just a picture).
The resolution you choose just has to do with how pixelated or clear the image looks. A lower resolution will be more pixelated. A higher resolution will be more clear, but it will be a larger file size.
Save map as image dialogue provides a very confusing combination of settings for scale, resolution (in dpi/dots per inch) and output width/height (in pixels). Frankly, these seem like contradictory options. The User Manual is not especially helpful here. I think your best bet to find the right settings will be by trial and error.