I don't know if it is a solution, but I suggest you automate it from the midi editor, editing the midi volume of the clip, instead of the track automation.
Doing it this way has another advantage. You can copy the volume drawing from a clip on one track and paste it into another clip on another track, if you want multiple tracks to behave similarly.
If what you want is to use a slider instead of drawing, you can do it from a midi controller with a slider and recording within the midi editor.
If you do not have a controller with a physical midi slider, you can use a smartphone or tablet connected by USB; there are many free apps that work as midi controllers.
I don't know if it is a solution, but I suggest you automate it from the midi editor, editing the midi volume of the clip, instead of the track automation.
Doing it this way has another advantage. You can copy the volume drawing from a clip on one track and paste it into another clip on another track, if you want multiple tracks to behave similarly.
If what you want is to use a slider instead of drawing, you can do it from a midi controller with a slider and recording within the midi editor.
If you do not have a controller with a physical midi slider, you can use a smartphone or tablet connected by USB; there are many free apps that work as midi controllers.
Or simpler, download the AppImage of VMPK virtual midi controller on your Linux and use it in the Qtractor midi input.
https://sourceforge.net/projects/vmpk/files/vmpk/0.8.10/