Wallace includes the option to download the prediction as a .tif. If it is incorrectly downloading as an html, perhaps with an error message, try restarting R and your browser. Make sure you have the following packages installed and updated: sf, mapview, webshot, raster.
Alternatively, if you are running code from the RMD, you can add the following line after you map the prediction:
raster::writeRaster(..., "/file/path/where/you/want/the/file/saved/NameYourFile.tif")
Don't forget to include the .tif at the end. Here is an example based on the screenshot you sent in the other post.
raster::writeRaster(predSel_Pp, "/file/path/where/you/want/the/file/saved/prediction_Pp.tif")
This will save it as a tif which can be opened using the raster upload in QGIS. The color ramp we use in Wallace is inverted RdYlBu.
Bethany