since GDAL 3.7 we can use vrt:// protocol with raster file/urls to apply many operations available to gdal_translate
so "vrt:///vsicurl/https://hella/big/raster.tif?outsize=10%,10%&expand=rgb" would on-the-fly produce VRT that decimates and expands a palette image to full RGB (watch out for special & etc use quotes)
works the same in cli or qgis or any R or Python package that uses GDAL
see doc for available args (note that vrt:// since 3.1 supported "bands=i,j,k")
https://gdal.org/drivers/raster/vrt.html#vrt-connection-string