After processing an image I exported it. The exported image contains so to see all exif/iptc tags I added to the original, except the GPS latitude, longitude and altitude. Strangely enough it does export GPSVersionID, GPSAltitudeRef, GPSTimeStamp and GPSDateStamp !
I didn't setup anything special, so I guess I left something out .. but what ?
Darktable 3.4.1 on a Linux Mint 20.1 installation.