QGIS 3 can’t seem to find external tools, including Python, and GDAL tools and some needed for Processing. There used to be settings for this but they’re gone.
For now the workaround is to go to the QGIS Preferences -> System.
- Under the Environment section, turn on Use Custom Variables.
- Add (+) a variable
- Select Prepend from the Apply popup
PATHfor the variable
- Enter the following for the value:
- Quit QGIS 3 and start it up again, GDAL tools and processing algorithms should find needed tools now.