I believe to have reported this issue before. If not: Yes please!

This type of integration is handled completely by iOS, there isn't really anything for us to do here. If it doesn't work for you it will be some form of issue with your Google Drive app!

There is something strange going on though. I can open a capture file from the Google drive app (tap the file, use "Open with...", select Capoture from the list of apps) and it will perfectly open in Capture mobile. It then appears in the Recent in Capture list within the Capture app itself and it stays available from there, no matter how long ago I've adressed that file (so even if it is not locally stored on the device). 

I can do the same from the iOS files app. Just not from the Browse tab in the Capture app. Only there, the files are greyed out as if they are not valid Capture files. So maybe there is something there there...

Thank you for the tip Floriaan. 

I can now open a capture file on ios by this way but a bit strange by the way...

Thank you